Cheese package, film, bag and process for packaging a CO2 respiring foodstuff

ABSTRACT

A packaged article, especially a respiring foodstuff such as cheese which generates or releases gas during storage, and a permeable multilayer biaxially oriented film suitable for allowing escape of such gas while minimizing transfer of oxygen across the film which has a thin layer of a blend of EVOH and nylon. In a preferred embodiment the low cost film having a high permeability to CO 2  and low O 2  permeability is used to package cheese.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part application of pendingapplication Ser. No. 08/044,669 filed Apr. 9, 1993 entitled “EVOH OxygenBarrier Stretched Multilayer Film” whose disclosure and teachings arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to packaged respiring foodstuffsand improvements in the art of packaging foodstuffs which produce gas,particularly CO₂ respiring foodstuffs, especially cheeses such as forexample emmental, gouda and edam.

[0003] Many hundreds of different kinds of cheese are made today. Thecheese making art is very old with evidence of cheese making as far backas 2300 B.C. Cheese is a cultured milk product i.e. typically a starterculture of bacteria which produce lactic acid as added to milk alongwith an enzyme called “rennin”. Rennin typically comes from rennet fromthe stomach of a calf or lamb, but may be derived from either animal orplant sources. The acid produced by the bacteria alters the pH of themilk to an acidity which causes a milk protein termed “casein” tocoagulate thereby forming curds. Rennin is an enzyme which facilitatescurd formation. Typically, both acid produced by bacteria and rennin areused together to form cheese curds and whey. Curds aggregate holding fatand whey in a network of protein. In cheese making this curd formationis usually followed by pouring off the whey and concentration of thecurds. To remove additional whey, curds may be cut, pressed, cookedand/or salted to produce what is termed “green” or unripened cheese.Here “green” refers to the youth or lack of aging of the cheese at thispoint in manufacture. The green cheese may then be aged or ripened foranywhere from a few days to up to four years or more depending upon thecheese variety. This ripening may continue even after packaging, but isgenerally slowed by holding cheese at lower refrigeration temperatures.

[0004] The above description relates to generally known processes formaking natural cheeses. Also known are “processed” cheeses which areground natural cheeses which typically mix unripened and ripened cheeseswith other ingredients such as added milk and stabilizers followed bypasteurization and usually packaging while hot.

[0005] In forming natural cheeses, specific molds or bacteria may beadded just prior to or during ripening to produce particular varietiesof cheese having different characteristics such as flavors, aromas,textures and appearance.

[0006] For example, blue cheeses are made by inserting a blue greenmold, Penicillium roquefort into the interior of the cheese. There arealso surface ripened cheeses such as brie and camembert which have anexterior surface coat of a white mold Penicillium camembert. Cheesessuch as brick and limburger are ripened by bacteria which are coated onthe surface of the cheese. The original starter culture bacteria alsomay provide distinctive characteristics for ripening. Bacteria added inthe starter culture is used for ripening in production of hard andsemi-hard cheeses such as parmesan, cheddar and gouda. Swiss typecheeses may also be ripened using the original starter culture, buttypically additional bacteria such as Propionibacter shermanii is addedto form the “eyes” of the cheese. In emmental or swiss-type cheesesthese “eyes” are formed as gas pockets of carbon dioxide (CO₂) which isgiven off in large amounts by the bacteria which is nourished by lacticacid (which is produced by other bacteria in the starter culture). Ongrading of swiss-type cheese, cheese graders (which may be licensed byvarious governmental entities) consider the amount, size and developmentof eyes as well as the cheese appearance including uniformity offirmness, and its flavor and aroma, shape, freedom from mold, color,size and saltiness.

[0007] After ripening, or after molding and pressing (for starterculture ripened varieties of cheeses), cheeses are coated or packaged toprevent physical damage, moisture loss and spoilage (eg. by miteinfestation or growth of undesirable molds or bacteria). Many packagingmaterials and preventive coatings are in use for contact with cheesesincluding: fat, cloth, wax, metal foils and plastic films and sheets.Waxes and resins in particular have been used for many years to coatdry, hard or semi-hard cheeses such as cheddar, cheshire, gouda, edamand danbo by dipping the cheese into melted wax. Cheese has also beenpackaged into polymer film under conditions which allow ripening of thecheese in the package.

[0008] In discussing plastic film packaging, various polymer acronymsare used herein and they are listed below. Also, in referring to blendsof polymers a colon (:) will be used to indicate that the components tothe left and right of the colon are blended. In referring to filmstructure, a slash “/” will be used to indicate that components to theleft and right of the slash are in different layers and the relativeposition of components in layers may be so indicated by use of the slashto indicate film layer boundaries. Acronyms commonly employed hereininclude:

[0009] PE—Polyethylene (an ethylene homopolymer and/or copolymer of amajor portion of ethylene with one or more α-olefins)

[0010] EVA—Copolymer of ethylene with vinyl acetate

[0011] PVDC—Polyvinylidene chloride (also includes copolymers ofvinylidene chloride, especially with vinyl chloride)

[0012] EVOH—A saponified or hydrolyzed copolymer of ethylene and vinylacetate

[0013] EAA—Copolymer of ethylene with acrylic acid Various publishedpatent documents disclose different types of cheese packages, packagingfilms and processes for packaging.

[0014] U.S. Pat. No. 1,925,443 (Gere) discloses flexible wrappers and aprocess for packaging uncured cheese wherein the cheese ripens or curesin the package. This patent states that “The package must be ofmoisture-proof and impervious material, and it must be so sealed as toexclude air, but at the same time, it must provide for the escape ofexcess carbon dioxide evolved in the course of fermentation”. Preferredwrappers include “cellulose viscose” or “cellulose acetate” which maysubsequently be coated with paraffin. Disadvantageously, manufacture ofthese films is complex, time consuming and expensive. Also, it isdifficult to adjust CO₂ permeabilities for use on different cheeses.

[0015] U.S. Pat. No. 2,494,636 (Stine) discloses a method of makingemmental (swiss) cheese which comprises applying a coat of extensible,flexible, fluid proof sealing material to the exterior surface of theuncured cheese to seal the surface prior to eye development followed bycuring under controlled pressure in an expandable mold. Suitable sealingmaterials are said to be wax, or a wrap of an elastic-flexible materialsuch as cellophane, the inner surface of which may be coated with aflexible and elastic wax. The packaging materials disclosed here havethe same disadvantages as described above for those materials disclosedin the Gere patent.

[0016] U.S. Pat. No. 2,871,126 (Smith et al.) discloses a method formanufacturing emmental type cheese which is also known as Swiss cheese.This patent refers to use of thermoplastic film as a moisture proof,fluid-proof material for wrapping the cheese after the brine step forcuring in molds. A disadvantage of this disclosed film is that themoisture proof wrapper does not have an adjustable CO₂ permeability.

[0017] U.S. Pat. No. 2,813,028 (Jackson, Jr.) discloses processes forproducing cheddar cheese. In one process green cheddar curd is extrudedinto preformed wrappers which may be made of cellulose based films suchas cellophane, rubber chloride based films or polyvinylidene chloridebased films such as saran. It is preferred that the films have thefollowing characteristics:

[0018] (1) substantially moisture proof i.e. having relatively lowmoisture vapor transmission rate to prevent drying out

[0019] (2) slightly permeable to carbon dioxide to permit normal curing

[0020] (3) cling or stick to cheese to prevent mold growth

[0021] (4) slightly extensible to improve cling between wrapper & cheeseby overfilling

[0022] (5) transparent or translucent to improve appearance.

[0023] The disclosed films suffer from disadvantageously, controllingCO₂ permeability by slightly opening the ends of the package. Thisremoves the physical, moisture and oxygen barrier at those openingsthereby subjecting the cheese to the deleterious effects of excessiveoxygen, loss of moisture and exposure to the environment.

[0024] Canadian Patent Application 2,053,707 (Mueller) discloseslaminate films for packaging soft cheeses such as camembert and brie.Known materials for packaging such soft cheese is said to includepolyethylenes with and without ethylene vinyl-acetate copolymers,polypropylenes, nylon/polyethylene laminates, and polyester/polyethylenelaminates. Oxygen and carbon dioxide transmission rates are said to be“of primary importance in the packaging of many soft cheeses, as well asother foods items which require a packaging material of high gaspermeability such as many fruits and vegetables”. (See page 1). Thedisclosed film of Mueller comprises a first film component (which isperforated) laminated to a gas permeable layer which include at leastone layer comprising butadiene styrene copolymers. Relative gas andmoisture transmission rates are said to be determined by the size andnumber of perforations in the first layer as well as the thickness andpermeability of the second layer.

[0025] In the examples, permeabilities of the film of Example 3 arestated as follows:

[0026] “The water vapor transmission rate averaged about 2.73 g/100 in²,24 hr. at 100° F. and 100% RH. The oxygen transmission rate averagedabout 4858.9 cm³/m² atm., 24 hrs. at 73° F. The carbon dioxidetransmission rate averaged about 30204.0 cm³/m², atm., 24 hrs. at 73°F.”

[0027] These films have a very high permeability to oxygen as well ascarbon dioxide and such extremely high oxygen permeability while perhapssuitable for mold cured cheeses is undesirable for hard or semi-hardcheeses such as emmental, gouda, edam and the like due to thepossibility of facilitating undesirable mold growth.

[0028] Canadian Patent Application No. 2,050,837 (Gillio-Tos et al.)discloses polymer mixtures of polyvinylidene chloride andpolyethyloxazoline which are purportedly useful in forming monolayer ormultilayer films having increased moisture permeability with nosubstantial change in permeability to oxygen or carbon dioxide. Thiscombination of properties purportedly is “indicative of utility inpackaging, for example, medical applications, casings and the curing ofnon-gassing cheeses such as parmesan” (page 3, last paragraph). A tableshows moisture, oxygen and carbon dioxide permeability rates. Thesefilms are made from chlorinated polymers which are increasingly moredifficult to dispose of or recycle as further discussed below.

[0029] EP 457 598 (Shah et al) discloses a polyamide based multilayerfilm for packaging cheese. This polyamide film is disclosed as having“an oxygen transmission rate of no more than 500 cc/M², 24 hrs., atm anda carbon dioxide transmission rate of at least 750 cc/m2, 24 hrs.,atm.”. Example 5 purportedly discloses a 1 mil (25.4 micron) thickbiaxially oriented film having a core layer comprising a blend of about70% EVOH and about 30% of a polyamide in combination with polypropyleneor propylene copolymer based outer layers and this film has a reportedshrinkage at 220° F. (104° C.) of 24% in two directions. The core layeris about 14% of the thickness of the film which would be 0.14 mil (3.6microns). Example 8 purportedly had outer layers of 90% linear mediumdensity polyethylene blended with 10% of an EVA-based masterbatch and acore layer which was a blend of 70% nylon and 30% EVOH, with the corelayer comprising 25% of the total film thickness. Disadvantageously, theshrinkage values of this film are achieved at high temperatures with thelowest reported measurement being made at 104° C. as denoted in theTable on page 8, and it is therefore to be expected that the shrinkagevalues at 90° C. and lower temperatures would disadvantageously be muchless. This results in films having high shrinkage only at undesirablyhigh temperatures.

[0030] Various monolayer and multilayer thermoplastic films have beencommercialized for packaging cheeses. Three to five layer films arecommon. Typical structures include: EVA/PVDC/EVA, EVA/EVA/PVDC/EVA,Ionomer/EVA/PVDC/EVA, and variations thereof where ethylene basedpolymers are blended into one or more of the EVA layers. Some cheesepackaging films are heat shrinkable at 90° C. and others are not. Someof the nonshrinking films have an oxygen barrier comprising one or morelayers of nylon or EVOH or a blend of EVOH with nylon. Such knownnonshrinking films include structures of the type EVA:PE/Nylon, EVA:PE/Nylon/EVOH/Nylon/EVA:PE, EVA:PE/PVDC/Nylon, EVA: PE/EVOH/Nylon, andEVA:PE/Nylon/EVA. The known nonshrinking EVOH containing films generallyhave a relatively thick EVOH containing layer, generally greater than0.5 mil (12.7 microns).

[0031] Of the foregoing nonshrinking films, those containing EVOH have atypical oxygen permeability of less than 10 cm³ per m² at 1 atm, 0%relative humidity and 23° C. and are considered high barrier films. Theterms “barrier” or “barrier layer” as used herein mean a layer of amultilayer film which acts as a physical barrier to gaseous oxygenmolecules. Physically, a barrier layer material will reduce the oxygenpermeability of a film (used to form the bag) to less than 70 cm³ persquare meter in 24 hours at one atmosphere, 73° F. (23° C.) and 0%relative humidity. These values should be measured in accordance withASTM standard D-1434.

[0032] Also known are films suitable for packaging cheese that are heatshrinkable at 90° C. which contain nylon or a blend of EVOH and nylon.Axially stretched, especially biaxially stretched, films which are “heatshrinkable” as that term is used herein have at least 10% unrestrainedshrinkage at 90° C. (10% in both the machine direction (M.D.) andtransverse direction (T.D.) for biaxially stretched films). Such knownfilms include structures of the following types: Ionomer/PE/Nylon,Ionomer/EVA/Nylon, EAA/Nylon:EVOH/Ionomer, and PE/EVOH:Nylon/PE. Some ofthese EVOH containing heat shrinkable films have an oxygen permeabilityin the high barrier range. A few heat shrinkable, EVOH-containing filmshave permeabilities which are outside the high barrier range such ase.g. about 30-35 cm³/m² or even as high as 150-170 cm³/m² at 1 atm, 0%relative humidity and 23° C.

[0033] As shown in the present specification, high barrier film (whethershrinkable or not) which are very good oxygen barriers typically alsohave very low carbon dioxide permeabilities which may bedisadvantageously low for packaging respiring articles such as cheeses,particularly hard and semi-hard cheeses. Packaging films which have lowpermeability to CO₂ are subject to pillowing when hermetically sealedaround an enclosed respiring article. If the respiration rate of theenclosed article exceeds the CO₂ transmission rate for permeating theenclosing film, “pillowing” will occur. Pillowing or “ballooning” refersto the inflation of the sealed film which typically causes the filmsurface to move away and out of contact with much of the surface of theenclosed article. For such respiring articles as foodstuffs e.g. hardand semi-hard cheeses, it is perceived that some customers viewpillowing as a defect and avoid purchase of refrigerated foodstuffshaving a pillowed container. Furthermore, it is believed that retentionof high concentrations of CO₂ about a respiring foodstuff may possiblyadversely affect the curing process itself, possibly delayingdevelopment of the desirable characteristics of the microbiologicalprocesses including e.g. full flavor and aroma development.

[0034] Also, the prior art EVOH-containing high permeability cheesefilms have several disadvantages for packaging respiring cheesesincluding one or more of the following: undesirably low shrink valuesparticularly at low temperatures e.g. 90° C. or lower, an undesirablynarrow heat sealing range, use of expensive resins such as ionomer inthe other layers, and poor optical properties such as high haze, lowgloss and/or streaks or lines which detract from the film appearance.Furthermore, known EVOH-containing cheese films have a disadvantageouslythick EVOH-containing layer which is often 2 to 10 times thicker thanthe present invention and difficult to process into an oriented film,difficult to make into a heat shrinkable film having high shrinkagevalues and shrink forces, especially in two directions, and whichrequires more material which may increase expense.

[0035] As shown by the above, many different multilayer film structureshave been and continue to be commercially made and used to packagecheeses. These structures all suffer from various disadvantages,especially with respect to packaging “respiring” cheeses i.e. thosecheeses which give off CO₂ gas.

[0036] For example, higher levels of CO₂ permeabilities with PVDCcontaining films require that the PVDC layer be heavily plasticized toachieve gas permeability. Such plasticizers may adversely affect otherfilm properties including processability, optical properties, andorientability.

[0037] Also, recycling of PVDC polymers is difficult, particularly wherethe waste polymer is mixed with other polymers having different meltingpoints. Attempts to remelt film containing PVDC frequently results indegradation of the PVDC component.

SUMMARY OF THE INVENTION

[0038] It is an object of the invention to provide a multilayer filmhaving a high carbon dioxide permeability and relatively low oxygenpermeability which is controlled by a thin core layer.

[0039] It is still another object of the invention to provide a filmhaving low permeability to water vapor.

[0040] It is another object of the invention to provide a multilayerfilm containing EVOH and having high shrinkage values at 90° C. or less.

[0041] It is a further object of the invention to provide anirradiatively crosslinked, CO₂ permeable multilayer film having anEVOH:nylon blend core layer having a broad impulse heat sealing voltagerange.

[0042] It is yet another object of the invention to provide an EVOHcontaining multilayer film having good optical properties.

[0043] It is a further object of the invention to provide achlorine-free packaging film.

[0044] It is an object of the invention to provide a film for packagingrespiring articles, particularly cheeses, which have reduced pillowingof the package after vacuum packaging.

[0045] It is another object of the invention to provide a packagedcheese using a multilayer film having a thin oxygen permeabilityretarding layer which is also permeable to carbon dioxide.

[0046] The above and other objects, benefits and advantages of theinvention will be apparent from the disclosure below which is exemplaryand nonlimiting. It is not necessary that each and every object listedabove be found in all embodiments of the invention. It is sufficientthat the invention may be usefully employed.

[0047] According to the present invention a gas releasing foodstuffespecially CO₂ respiring cheese, is packaged in a multilayer,thermoplastic, flexible film of at least five layers having a thin corelayer (about 0.05 to-0.1 mil (1.7-2.54 microns) which comprises a blendof about 20-70 weight percent nylon and about 30-80% of an ethylenevinyl alcohol copolymer having an ethylene content of about 38 molepercent or higher. Preferably the inventive film will be heat sealablehaving at least one layer which is crosslinked, preferably byirradiation. In a preferred highly useful embodiment of the invention,the film will be heat shrinkable at temperatures such as 90° C. orlower, and may have shrinkage values in one or both of the MD and TDdirections of at least about 20%, and advantageously e.g. for packagingcheese may be at least 30%.

[0048] In one embodiment of the invention, a packaged respiring naturalcheese such as emmental, jarlsberg, edamer, butterkase, gouda or edam isprovided where an EVOH:nylon 6/66 copolymer (here 6/66 is used to denotea copolymer of nylon 6 and nylon 66) blend core layer of the film hasthe relative amounts of nylon and EVOH adjusted to provide the desiredlevel of CO₂ permeability and O₂ barrier properties. Such a film neednot be perforated, and preferably is unperforated, yet a high level ofCO₂ permeability may be obtained without perforations.

DETAILED DESCRIPTION OF THE INVENTION

[0049] The inventive film, bag, process and package of the presentinvention may be used as a CO₂ permeable, oxygen barrier film forholding a respiring natural cheese during curing or for packaging forsale of such a cheese after the predetermined curing period. Aftercuring of a cheese such as emmental, the cheese which may be a largeblock of up to forty pounds (18.2 Kg) or more is often cut up intosmaller sizes such as 10 or 7 pound (4.5-3.2 Kg) portions or less forsale to commercial establishments such as hotels, restaurants or otherinstitutions or for retail sale through deli counters or to individualconsumers. Forty pound (18.2 Kg) blocks of cheese are frequentlypackaged in thermoplastic bags having a flat width of 18-22 inches(46-56 cm) while smaller weights are typically packaged in bags having asmaller flatwidth e.g. of less than 10 inches (25.4 cm) for weights of 5pounds (11 Kg) or less. The present invention may be employed as bags inthe various typical sizes. By “flatwidth” is meant the transverse widthof a flattened tubular film. The flatwidth is also equal to ½ of thecircumference of the tubular film.

[0050] The invention has particular utility in packaging natural cheese.Cheese as it is produced from milk with curds that are only cut orpressed is said to be natural (as further discussed above) and may becontrasted with “process” cheese which is made from natural cheese e.g.by grinding, heating and pasteurizing natural cheese with additiveswhich may include milk, water, emulsifiers and/or preservatives.Pasteurization stops or inhibits the aging/ripening process which givesoff CO₂. Therefore, the CO₂ permeable films of the instant invention areparticularly advantageous for enclosing natural respiring cheesesbecause the inventive films allowed CO₂ to escape by permeation acrossthe film wall. At the same time the present films and bags madetherefrom are much less permeable to oxygen and this is an advantagebecause the presence of large amounts of oxygen is believed tofacilitate growth of undesirable molds.

[0051] The present invention is particularly well adapted to packagingrespiring cheeses, especially cheeses having eyeholes. Eyeholes incheese are produced by pockets of carbon dioxide (CO₂) which isgenerated by CO₂ producing bacteria such as Propionibacter shermanii.

[0052] The invention may be suitably employed with hard cheesesincluding those having eyeholes which are typically round such asemmental, jarlsberg, gruyere, herregaardsost, danbo, asiago,viereckhartkase, bergkase and samsoe, as well as those cheeses whichtypically have irregular holes such as cheshire, maribo, svecia andmanchego, and those cheeses which generally have no or few holes such ascheddar, and provolone. The invention may also be suitably employed withsemi-hard cheeses including those having small eyeholes such as gouda,edam, fontina, raclette and those typically having irregular eyeholessuch as trappist, tilsit and havarti, and even those which typicallyhave no holes such as butter cheese (butterkase), cantal, St. Paulin andfeta.

[0053] Advantageously, the relative amounts of EVOH polymer and nylonpolymer may be adjusted according to the present invention to providefilms, bags and packages having various permeabilities to gasesincluding CO₂. An example of suitable CO₂ permeabilities for variouscheeses is given in Table A below. TABLE A High CO₂ Permeability(400-600 cm³/m² at 5° C. and 0% RH per 24 hr at 1 atmosphere) emmental(Swiss) jarlsberg herregaaddsost svecia maribo samsoe Medium CO₂Permeability (200-400 cm³/m² at 5° C. and 0% RH per 24 hr at 1atmosphere) raclette Low CO₂ Permeability (100-200 cm³/m² at 5° C. and0% RH per 24 hr at 1 atmosphere) cheddar gouda edam edamer butterkase

[0054] Embodiments of the present invention for use in high CO₂permeability applications will generally use a core layer having agreater amount of nylon (>50 to 70%) and lesser amounts of EVOHcopolymer (30 to <50%) to produce a film having higher CO₂ permeability.The high permeability film will also utilize an EVOH having an ethylenecontent of about 48 mole percent or higher because EVOH copolymershaving lower ethylene contents have been found to produce films whichare more gas impermeable. Preferably the oxygen permeabilities of thehigh CO₂ permeability films and bags of the present invention will beless than 800 cm³/m² and greater than 500 cm³/m² at 24 hours, 1atmosphere, 0% relative humidity and room temperature (20-23° C.).

[0055] Embodiments of the present invention for use in low CO₂permeability applications will generally use a core layer having agreater amount of EVOH (70-80%) and lesser amounts of nylon (20-30%) toproduce a film having a low CO₂ gas transmitting rate, particularly whenusing an EVOH copolymer having an ethylene content of about 48 molepercent. However, EVOH copolymers having lower contents of ethylene e.g.of 44 mole % or as low as 38 mole % may be employed to make low CO₂permeability films which are suitable for packaging articles whichrespire low levels of CO₂ such as gouda, edamer, edam, butterkase andcheddar cheeses, by blending lower amounts of EVOH with higher amountsof nylon. The appropriate blend proportions to achieve the desired levelof gas permeability may be determined in view of the presentspecification without undue experimentation. Even these low CO₂permeability films made according to the present invention will have anoxygen permeability of about 40 cm³/m² or higher at 24 hours, 1atmosphere, 0% relative humidity and room temperature, preferably theoxygen transmission rate will be less than about 75 cm³/m².

[0056] Embodiments of the present invention for use in medium CO₂permeability applications to adjust and control the CO₂ permeability ofthe film to a level between that of high and low CO₂ permeable films ofthe invention will generally use nylon and EVOH in amounts between thoseused for high and low permeability films i.e. >30-50 nylon blended with50 to <70% EVOH when using an EVOH having an ethylene content of about48 mole %. As noted above, use of EVOH resins having a lesser ethylenecontent e.g. of about 38 mole % or 44 mole % may require additionalnylon to achieve the desired permeability. It should be apparent fromthe above that use of EVOH resins containing an ethylene content greaterthan 48 mole % may require less nylon to achieve equivalentpermeabilities relative to the 48 mole % EVOH blends discussed above.For these medium CO₂ permeability films, the oxygen transmission rate isalso 40 cm³/m² or higher at 24 hours, 1 atmosphere, 0% relative humidityand at room temperature (about 20-23° C.).

[0057] In addition to changing the proportion of the blended amounts ofEVOH and nylon in the core layer to adjust the gas e.g. CO₂ permeabilityof the films of the invention, the thickness of the core layer may alsobe varied from about 0.05 to about 0.10 mils (1.3-2.54 microns). Also,while it is preferred that the core layer consist essentially of nylonand EVOH, the present invention recognizes the possibility that theother additives including polymers e.g. other nylons may be blended intothe core layer to purposefully affect core layer properties such as gaspermeability or moisture resistance.

[0058] Advantageously, the present invention permits ripening ofCO₂-producing cheeses in a thermoplastic multilayer film having a thincore layer of a blend of EVOH with nylon with little or no weight lossduring ripening. The moisture barrier properties of the film minimizeweight loss from moisture permeation through the film after packaging.Films of the present invention having water vapor transmission ratesless than 30 grams per square meter per 24 hours at 100° F. (37.8° C.)under ambient pressure at (˜1 atmosphere) have been found to havedesirably low weight loss from moisture permeation through the film.

[0059] Also, the oxygen barrier properties of the inventive film reducesor eliminates losses of cheese caused by scraping off mold fromcontaminated surfaces before repackaging for retail sale. Product lossesand sensory defects due to mite infection and mold growth are alsoprevented by use of the film according to the present invention. Thepresent invention may be beneficially used as a ripening filmparticularly for rindless cheese where rinds having surface molds orbacteria to give particular flavor and odor sensory characteristics tothe cheese are not employed. The inventive films and bags areparticularly useful for packaging cheese, but may also be employed aspackaging for a wide variety of food and non food articles.

[0060] Some of the benefits of the inventive film include: relativelylow permeability to oxygen and water vapor, particularly in combinationwith higher CO₂ permeability; controlled permeability (and highpermeability if desired) to carbon dioxide without perforations in thefilm; resistance to degradation by food acids, salts and fat; highshrinkage values at low temperatures (90° C. or lower); residual shrinkforce which maintains a low level of oxygen contact with the foodsurface after opening; good heat sealability especially over a broadvoltage range on commercial sealers; low levels of extractables withcompliance with governmental regulations for food contact; delaminationresistance; low haze; high gloss; easy to remove from an enclosedfoodstuff such as cheese; does not impart off tastes or odors topackaged food; good tensile strength; a surface which is printable; andgood machinability.

[0061] Advantageously, a preferred embodiment of the invention has ahigh CO₂ permeability at 5° C. with relatively low O₂ and low watervapor permeabilities in combination with good low temperature (90° C. orless) shrinkage values. In an especially preferred embodiment theinventive film has at least 20% (more preferably about 30% or higher)shrinkage values in at least one direction and preferably two directionsat 90° C. or less. Also, preferred films are heat sealable over a broadvoltage range, and preferably heat shrinkable at low temperatures incombination with such broad range heat sealability.

[0062] The invention in all of its embodiments comprises or utilizes amultilayer thermoplastic polymeric flexible film of 10 mils (254microns) or less having an unusually thin core layer containing a blendof EVOH and nylon. This EVOH:nylon blend layer controls the gaspermeability of the film. Such films will preferably have a thickness ofabout 2-2.5 mils (50.8-63.5 microns) although suitable films e.g. forpackaging foodstuffs as thick as 4 mils (101.6 microns) or as thin as 1mil (25.4 microns) may be made. Typically films will be between about1.5-3 mil (38.1-76.2 microns). Especially preferred for use as bags orfilms for packaging articles including foodstuffs, e.g. cheeses, arefilms wherein the multilayer film has a thickness of between about 2 to2.5 mils (50.8-63.5 microns). Such films have good abuse resistance andmachinability. Films thinner than 2 mils are more difficult to handle inpackaging processes. Advantageously, preferred films are heatshrinkable. Preferred films may also provide a beneficial combination ofone or more or all of the properties including high gloss, highshrinkage values at 90° C. or less, good machinability, good mechanicalstrength and good relatively low oxygen barrier and water barrierproperties with desirably high CO₂ permeabilities.

[0063] The expression “ethylene vinyl acetate copolymer” (EVA) as usedherein refers to a copolymer formed from ethylene and vinyl acetatemonomers wherein the ethylene derived units (monomer units) in thecopolymer are present in major amounts (by weight) and the vinyl acetatederived units (monomer units) in the copolymer are present in minor, byweight, amounts.

[0064] The expression very low density polyethylene (“VLDPE”) sometimescalled ultra low density polyethylene (“ULDPE”), refers to linearpolyethylenes having densities below about 0.915 g/cm³ and according toat least one manufacturer, possibly as low as 0.86 g/cm³. Thisexpression does not include ethylene alpha olefin copolymers ofdensities below about 0.90 g/cm³ with elastomeric properties andreferred to as elastomers. Some elastomers are also referred to by atleast one manufacturer as “ethylene alpha olefin plastomers”, but othermanufacturers have characterized VLDPE as an ethylene α-olefin withplastomeric properties. However, as hereinafter explained, ethylenealpha elastomers or olefin plastomers may be advantageously used in thepractice of this invention as a minor constituent in certain layers ofthis multilayer film. VLDPE does not include linear low densitypolyethylenes (LLDPE) which have densities in the range of 0.915-0.930gm/cm³. VLDPE's as the term is used herein may be made by solution orfluidized bed processes using a variety of catalysts includingZiegler-Natta or metallocene catalysts.

[0065] VLDPE comprises copolymers (including terpolymers) of ethylenewith alpha-olefins, usually 1-butene, 1-hexene or 1-octene, and in someinstances terpolymers, as for example of ethylene, 1-butene and1-hexene. A process for making VLDPEs is described in European PatentDocument publication number 120,503 whose text and drawing are herebyincorporated by reference into the present document.

[0066] As for example described in Ferguson et al. U.S. Pat. No.4,640,856 and Lustig et al. U.S. Pat. No. 4,863,769, VLDPEs are capableof use in biaxially oriented films and have superior properties tocomparably made films having LLDPEs. These superior properties includehigher shrink, higher tensile strength and greater puncture resistance.

[0067] Suitable VLDPEs include those manufactured by Dow ChemicalCompany, Exxon Chemical Company and Union Carbide Corporation.

[0068] EVOH is prepared by the hydrolysis (or saponification) of anethylene-vinyl acetate copolymer, and it is well known that to be aneffective oxygen barrier, the hydrolysis-saponification must be nearlycomplete, ie. to the extent of at least 97%. EVOH is commerciallyavailable in resin form with various percentages of ethylene and thereis a direct relationship between ethylene content and melting point.

[0069] In the practice of this invention, the EVOH component of the corelayer has a melting point of about 175° C. or lower. This ischaracteristic of EVOH materials having an ethylene content of about 38mole % or higher. EVOH having an ethylene content of 38 mole % has amelting point of about 175° C. With increasing ethylene content themelting point is lowered. Also, EVOH polymers having increasing molepercentages of ethylene have greater gas permeabilities. A melting pointof about 158° C. corresponds to an ethylene content of 48 mole %.Preferred EVOH materials will have an ethylene content of 48 mole %.EVOH copolymers having higher ethylene contents may be employed and itis expected that processability and orientation would be facilitated,however gas permeabilities, particularly with respect to oxygen maybecome undesirably high for certain packaging applications which aresensitive to mold growth in the presence of oxygen.

[0070] It has been discovered that the inventive film with all of itsadvantages can only employ nylon 6/66 as the polyamide in the polymerblend of the oxygen barrier layer. Nylon 6/66 is a copolymer of nylon 6and nylon 66. Nylon 6 is polyepsilon caprolactam. Nylon 66 is thepolymer derived from adipic acid and hexamethylene diamine.

[0071] Nylon 6/66 is manufactured by different companies, in someinstances with different percentages of the two monomers, possibly bydifferent methods and presumably with different operating parameters.Accordingly, the properties of various nylon 6/66 copolymers may differsignificantly. For example, the melting temperature decreases as thenylon 66 content is increased from 5% to 20 mole %.

[0072] When other nylons such as type 6,12 are used as the polyamide inthe polymer blend of the oxygen barrier layer, numerous gels develop inthe core layer of the five layer film and in some instances cracksdevelop. The gels may be due to EVOH-nylon 6,12 incompatibility orchemical reaction between the two polymers. The cracks probably developbecause the polymer blend is not stretching uniformly during theorientation. These numerous gels and cracks are unacceptable in filmsfor commercial use to package foodstuffs and indicate potential weakspots in the film integrity and permeability properties.

[0073] A preferred nylon is a nylon 6/66 copolymer having a meltingpoint of about 195° C., which has a reported nylon 6 component contentof about 85 mole % and a nylon 66 component content of about 15 mole %and which is commercially available from Allied Chemical Co. ofMorristown, N.J., U.S.A. under the trademark Nylon 1539.

[0074] It has been discovered that a workable film may be obtained bysubstituting nylon 11 (poly ω-aminoundecanoic acid) for the nylon 6/66copolymers in the present invention. Such film has many of theadvantages of the present invention including good low temperatureshrink values and desirable CO₂ and O₂ permeabilities, but the opticalproperties are not as excellent and noticeable lines may appear in thefilm, notwithstanding desirably low haze and high gloss values.

[0075] Advantageously, films of the present invention may have low hazee.g. less than 10 and preferably less than 5%, and high gloss e.g.greater than 65 Hunter Units (H.U.) and preferably greater than 75 H.U.

[0076] The inventive article is preferably a heat shrinkable multilayerfilm which must have at least five layers. These five essential layersare termed the first outer layer, the first adhesive layer, the corelayer, the second adhesive layer, and the second outer layer. The firstouter layer and second outer layer are disposed on opposing sides of thecore layer and are attached thereto by the first and second adhesivelayers, respectively. These five layers are essential to the film ofthis invention. When the film is in tube or bag form these layerscomprise the wall of the tube or bag. This wall in cross-section has thefirst outer layer comprising an inner layer disposed closest to thetube's (or bag's) interior surface with the second outer layer disposedclosest to the tube's (or bag's) exterior surface.

[0077] It is contemplated according to the present invention thattubular films having more than five layers may be constructed and thatsuch additional layers may be disposed as additional intermediate layerslying between the core layer and either or both of the inner and outerlayers, or these additional layers may comprise one or more surfacelayers and comprise either or both the interior or exterior surface ofthe tube. Preferably, the first outer layer will comprise the inner orinterior surface layer of the tube where in use it will contact afoodstuff encased by the tube. Beneficially, this first outer layer willbe heat sealable to facilitate formation of bags and hermetically sealedpackages. Advantageously, the first outer layer as the interior or innersurface layer will, when used to package foodstuffs, be suitable forcontact with foodstuffs containing protein, water and fat withoutevolving or imparting harmful materials, off tastes or odors to thefoodstuff. In a preferred embodiment, the invention provides a filmsuitable for packaging cheeses, particularly cheeses which give offcarbon dioxide gas (also termed “respiring”) while packaged, such asemmental (swiss), gouda or edam. Beneficially, in the present inventionthe first outer layer may be the interior surface layer and may consistessentially of an ethylene vinyl acetate copolymer such as an EVA havingabout 10.5% by weight of vinyl acetate (10.5% VA) which facilitatesorientation to produce a film having high shrinkage values especially at90° C. or lower (e.g. 85° C. or 80° C.). Advantageously, the heatsealing layer and indeed the entire film may be free of ionomer polymeryet provide entirely satisfactory performance without the added expenseof using costly ionomer resin. If desired, an ionomeric resin may beused either alone or blended in one or more of the layers but such useis unnecessary to produce a film suitable for packaging respiringcheeses.

[0078] Also, it is preferred that the second outer layer will comprisethe exterior surface of the tube or bag. As the exterior surface layerof the tube or bag, the outer layer should be resistant to abrasions,abuse and stresses caused by handling and it should further be easy tomachine (i.e. be easy to feed through and be manipulated by machinese.g. for conveying, packaging, printing or as part of the film or bagmanufacturing process). It should also facilitate stretch orientationwhere a high shrinkage film is desired, particularly at low temperaturessuch as 90° C. and lower.

[0079] Advantageously, either or both of the first and second outerlayers may be predominantly comprised of ethylene homopolymers orcopolymers having at least 50% or higher ethylene content and may alsobe free of polypropylene or propylene copolymers having a propylenecontent of 50% or more, and films made with such outer layers accordingto the present invention may be oriented either uniaxially or biaxiallyby axial stretching at temperatures low enough to produce lowtemperature high shrink films. Such heat shrinkable films will have atleast 10% shrink in at least one direction at 90° C., but preferablywill have at least 20% shrink at 90° C. in at least one direction(preferably both directions) and advantageously may have at least 30%shrink at 90° C. in at least one direction, but preferably both M.D. andT.D. directions, and beneficially may have at least 15% (more preferablyat least about 20%) shrink at 80° C. in at least one and preferably bothM.D. and T.D. directions. The outer layers function to protect the corelayer from abuse and may also protect it from contact with moisturewhich may impact or alter the gas barrier properties of the core layerEVOH and/or nylon.

[0080] Beneficially, in the present invention there are intermediateadhesive layers on either side of the core layer with these intermediateadhesive layers adhering the core layer to both the inner and outerlayers. In a preferred embodiment the EVOH:nylon blend core layerdirectly adheres to the first and second adhesive layers which in turnare directly adhered respectively to the inner and outer layers. In amost preferred embodiment the film article consists essentially of fivepolymeric layers viz the inner layer, the first adhesive layer, the corelayer, the second adhesive layer and the outer layer. This preferredembodiment provides a desirable combination of properties such as lowmoisture permeability, relatively low O₂ permeability in combinationwith relatively high CO₂ permeability, high gloss, good mechanicalstrength, chlorine-free construction, and desirable shrink forces in alow temperature heat shrinkable, multilayer packaging film which isdelamination resistant and can be oriented without requiring addition ofprocessing aids or plasticizers to the EVOH:nylon core layer. Preferablythe core layer will be free of such processing aids or plasticizers.

[0081] Typical layer thicknesses for the inventive heat shrinkable filmmay be about 5-70% first outer (or inner) layer, 2-10% first adhesivelayer, 2-10% core layer, 2-10% second adhesive layer and 20-35% secondouter layer, although films with differing layer ratio thicknesses arepossible. The function of the first outer layer (which is typically theinner layer in a tubular construction) is to provide a layer which hashigh shrinkage capability and a surface which is heat sealable to itself(or to the second outer layer where a lap seal is desired) oncommercially available equipment and (for food packaging) to provide ahygienic surface for contact with the foodstuff which is typically acheese, such as a semi-soft or semi-hard or hard cheese and especially aCO₂ respiring cheese such as edam, gouda or emmental (swiss). In thepresent invention, to fulfill the second and third functions thethickness of the inner layer need not be great, but for shrinkabilityand ease of processing this layer will preferably be the thickest of thelayers and in a preferred embodiment the major thickness (>50%) of theentire film. Alternatively, another layer may be the shrink controllinglayer or a shrink controlling layer may be added on either side of thecore layer. In such alternative embodiments the first outer layer forsealing and food contact may be made very thin i.e. 5% or less of thetotal thickness. It is important that this heat sealable layer becontinuous, e.g. over the inner surface of the tube, and that it beextruded at a sufficient thickness to allow heat sealing (if desired) aswell as being thick enough to accommodate the desired degree ofstretching without bursting or failure.

[0082] Preferably, the first outer layer is a heat sealing layer whichallows the film to be formed into bags. By the term “heat sealing layer”is meant a layer which is heat sealable to itself, i.e., capable offusion bonding by conventional indirect heating means which generatesufficient heat on at least one film contact surface for conduction tothe contiguous film contact surface and formation of a bond interfacetherebetween without loss of the film integrity. Advantageously, thebond interface must be sufficiently thermally stable to prevent gas orliquid leakage therethrough when exposed to above or below ambienttemperatures during processing of food within the tube when sealed atboth ends, i.e., in a sealed bag form. Finally, the bond interfacebetween contiguous inner layers must have sufficient physical strengthto withstand the tension resulting from stretching or shrinking due tothe food body sealed within the tube.

[0083] The first outer layer especially as the inner layer of a tubeaccording to the present invention also provides good machinability andfacilitates passage of the film over equipment (e.g. for insertingfoodstuffs such as cheese). This layer may be coated with an anti-blockpowder. Also, conventional antiblock additives, polymeric plasticizers,or slip agents may be added to the first outer layer of the film or itmay be free from such added ingredients. In one embodiment of theinvention the first outer layer consists essentially of an EVAcopolymer.

[0084] Advantageously, the core layer functions as a controlled gasbarrier, and provides the desired CO₂ and O₂ permeabilities for thearticle (e.g. foodstuff) to be packaged. It should also provide goodoptical properties when stretch oriented, including low haze and astretching behavior compatible with the layers around it for ease oforientation. It is essential that the thickness of the core layer beless than about 0.10 mil (2.54 microns) and greater than about 0.05 mil(1.27 microns) to provide the desired combination of the performanceproperties sought e.g. with respect to carbon dioxide permeability,oxygen permeability, shrinkage values especially at low temperatures,ease of orientation, delamination resistance and cost. Preferably, thethickness of the core layer will also be less than about 5% of the totalthickness of the multilayer film suitable thicknesses are less than 10%e.g. from 2 to 10% of the total film thickness.

[0085] The core layer must be a blend of EVOH and nylon which containsabout 20-70 wt. % of nylon and about 30-80 wt. % of EVOH copolymer. Useof lower amounts of nylon (less than 20% and particularly less than 15%)results in a tendency for the core layer to crack (sometimes referred toas “line-drawing”) rather than stretch uniformly during orientation.This is in part due to the relatively brittle nature of EVOH polymerscompared to e.g. EVAs and PEs. Similarly, at EVOH levels above 80% thetendency for such cracking, and formation of optical defects andpotential core layer discontinuities is undesirably greater. At EVOHlevels below 30% the oxygen gas permeability of the film tends to becomeundesirably excessive which may lead to an enhanced probability of moldgrowth due to increased oxygen permeability e.g. on cheeses packaged ina film of such construction. Preferably a high to medium high CO₂permeable film will have an EVOH:nylon content between about 30:70percent and 60:40 percent while a medium low to low CO₂ permeable filmwill have an EVOH:nylon content of between about 60:40 percent and 80:20percent.

[0086] The outer layer provides mechanical strength, abrasion resistanceand resists burn through during heat sealing. This outer layer istypically sufficiently thick to provide support and impart strength tothe packaging film wall in order to withstand the shrinking operation,handling pressures, abrasion, and packaging with a foodstuff such ascheese. Advantageously, it may comprise a polyethylene i.e. an ethylenehomopolymer or a copolymer of ethylene with a minor proportion of one ormore alpha-olefins, which may provide a water vapor barrier whichresists moisture permeation. High moisture barrier properties aredesirable to avoid weight loss and undesirable drying of the cheesewhich may deleteriously affect the desired cheese sensory propertiesincluding texture, mouth feel, taste and appearance.

[0087] The multilayer film of the invention may be made by conventionalprocesses including e.g. slot cast or blown film processes, butpreferably will be made by an orientation process, especially underconditions to produce a film which is heat shrinkable at 90° C. or less.Nonshrink films according to the present invention may be used asoverwraps, stretch wraps or as industrial plastic wrap. Shrink filmsaccording to the present invention may be used in value addedapplications. For example, a packaged foodstuff such as cheese having aheat shrinkable film enclosure according to the invention willadvantageously cling to the foodstuff even after opening. Non-shrinkbags have a tendency to fall away from the sides of the enclosed product(e.g. cheese) once the vacuum is broken by either intentional oraccidental opening. Once the film separates from the enclosed articlesurface, oxygen comes into contact with the article surface and productdefects on susceptible products such as growth of undesired mold oncheese may occur. Many prior art films and bags are nonshrink bags whichsuffer from this defect thereby causing spoilage and waste when used topackage perishable foodstuffs such as cheese. Undesired mold is oftencut away or scraped from a cheese surface causing product loss.Advantageously, in one preferred embodiment the present inventionprovides a shrink film which eliminates or minimizes such losses whileutilizing film resins of lower cost than some prior art multilayershrink films which have thick EVOH containing layers and/or utilizingexpensive ionomer resins and/or require relatively thick adhesive layers(each intermediate adhesive layer being >10-15% of the total filmthickness) on either side of the core layer to orient the film. Itshould also be noted that resins such as anhydride modified polyolefinare relatively expensive and use of thick adhesive layers undesirablyincreases the cost of multilayer films.

[0088] The five layer film of this invention may be manufactured bycoextrusion of all layers simultaneously for example as described inU.S. Pat. No. 4,448,792 (Schirmer) or by a coating lamination proceduresuch as that described in U.S. Pat. No. 3,741,253 (Brax et al.) to forma relatively thick primary multilayer extrudate either as a flat sheetor, preferably, as a tube. This sheet or tube is oriented by stretchingat orientation temperatures which are generally below the melting pointsfor the predominant resin comprising each layer oriented. Stretchorientation may be accomplished by various known methods e.g. tenteringwhich is commonly employed to orient sheets, or by the well-knowntrapped bubble or double bubble technique for orienting tubes as forexample described in U.S. Pat. No. 3,456,044 (Pahlke). In this bubbletechnique an extruded primary tube leaving a tubular extrusion die iscooled, collapsed and then preferably oriented by reheating andinflating to form an expanded secondary bubble which is again cooled andcollapsed. Preferred films are biaxially stretched. Transverse direction(TD) orientation is accomplished by the above noted inflation toradially expand the heated film which is cooled to set the film in anexpanded form. Machine direction (MD) orientation is preferablyaccomplished with the use of sets of nip rolls rotating at differentspeeds to stretch or draw the film tube in the machine direction therebycausing machine direction elongation which is set by cooling.Orientation may be in either or both directions. Preferably, a primarytube is simultaneously biaxially stretched radially (transversely) andlongitudinally (machine direction) to produce a multilayer film which isheat shrinkable at temperatures below the melting points of the majorpolymeric components, e.g. at 90° C. or lower. Axially stretched,especially biaxially stretched, films which are “heat shrinkable” asthat term is used herein have at least 10% unrestrained shrinkage at 90°C. (10% in both the machine direction (M.D.) and transverse direction(T.D.) for biaxially stretched films).

[0089] The general annealing process by which biaxially stretched heatshrinkable films are heated under controlled tension to reduce oreliminate shrinkage values is well known in the art. If desired, filmsof the present invention may be annealed to produce lower shrinkagevalues as desired for the particular temperature. The stretch ratioduring orientation should be sufficient to provide a film with a totalthickness of between about 1.5 and 4.0 mils. The MD stretch ratio istypically 3-6 and the TD stretch ratio is also typically 3-6. An overallstretch ratio (MD stretch multiplied by TD stretch) of about 9×-36× issuitable.

[0090] The preferred method for forming the multilayer film iscoextrusion of the primary tube which is then biaxially oriented in amanner similar to that broadly described in the aforementioned U.S. Pat.No. 3,456,044 where the primary tube leaving the die is inflated byadmission of a volume of air, cooled, collapsed, and then preferablyoriented by reinflating to form a secondary tube termed a “bubble” withreheating to the film's orientation (draw) temperature range. Machinedirection (MD) orientation is produced by pulling or drawing the filmtube e.g. by utilizing a pair of rollers traveling at different speedsand transverse direction (TD) orientation is obtained by radial bubbleexpansion. The oriented film is set by rapid cooling. In the followingexamples, all five layers were coextruded as a primary tube which wascooled upon exiting the die by spraying with tap water. This primarytube was then reheated by radiant heaters with further heating to thedraw temperature (also called the orientation temperature) for biaxialorientation accomplished by an air cushion which was itself heated bytransverse flow through a heated porous tube concentrically positionedaround the moving primary tube. Cooling was accomplished by means of aconcentric air ring.

[0091] In a preferred process for making films of the present invention,the resins and any additives are introduced to an extruder (generallyone extruder per layer) where the resins are melt plastified by heatingand then transferred to an extrusion (or coextrusion) die for formationinto a tube. Extruder and die temperatures will generally depend uponthe particular resin or resin containing mixtures being processed andsuitable temperature ranges for commercially available resins aregenerally known in the art, or are provided in technical bulletins madeavailable by resin manufacturers. Processing temperatures may varydepending upon other process parameters chosen. However, variations areexpected which may depend upon such factors as variation of polymerresin selection, use of other resins e.g. by blending or in separatelayers in the multilayer film, the manufacturing process used andparticular equipment and other process parameters utilized. Actualprocess parameters including process temperatures are expected to be setby one skilled in the art without undue experimentation in view of thepresent disclosure.

[0092] As generally recognized in the art, resin properties may befurther modified by blending two or more resins together and it iscontemplated that various resins may be blended into individual layersof the multilayer film or added as additional layers, such resinsinclude ethylene-unsaturated ester copolymer resins, especially vinylester copolymers such as. EVAs very low density polyethylene (VLDPE),linear low density polyethylene (LLDPE), low density polyethylene(LDPE), high density polyethylene (HDPE), nylons, ionomers,polypropylene or other esters. These resins and others may be mixed bywell known methods using commercially available tumblers, mixers orblenders. Also, if desired, well known additives such as processingaids, slip agents, antiblocking agents, pigments, etc., and mixturesthereof may be incorporated into the film.

[0093] In some preferred embodiments of the invention it is preferred tocrosslink the entire film to broaden the heat sealing range. This ispreferably done by irradiation with an electron beam at dosage levels ofat least about 2 megarads (MR) and preferably in the range of 3-5 MR,although higher dosages may be employed. Irradiation may be done on theprimary tube or after biaxial orientation. The latter, calledpost-irradiation, is preferred and described in U.S. Pat. No. 4,737,391(Lustig et al.). An advantage of post-irradiation is that a relativelythin film is treated instead of the relatively thick primary tube,thereby reducing the power requirement for a given treatment level.

[0094] Alternatively, crosslinking may be achieved by addition of achemical crosslinking agent or by use of irradiation in combination witha crosslinking enhancer added to one or more of the layers, as forexample described in U.S. Pat. No. 4,055,328 (Evert et al.). The mostcommonly used cross-linking enhancers are organic peroxides such astrimethylpropane and trimethylacrylate.

[0095] It will be seen from the following description that the fivelayer film of this invention has a very thin EVOH-nylon blend core layerthickness of between about 0.05 and about 0.1 mil yet provides acontrolled carbon dioxide (CO₂) permeability of between about 75 to 600cm³/m² measured at 5° C., 0% relative humidity, for 24 hours at 1atmosphere and relatively low oxygen transmission rate which ispreferably less than 800 cm³/m² at 23° C. for 24 hours at 1 atmosphereand 0% relative humidity. This has been accomplished with asubstantially thinner barrier layer containing the relatively expensiveEVOH than heretofore proposed films of this type. Yet the totalthickness of the multilayer film is between about 1.0 and about 4.0mils, the same as the conventional multilayer oxygen-moisture barrierfilms currently used in cheese packaging. The relative ratio of EVOH tonylon may be modified to select the desired CO₂ permeability. Suitableranges for high CO₂ permeable film may range from 30 to 60% EVOH and40-70% nylon. Suitable ranges for low CO₂ permeable films may range from60 to 80% EVOH and 20-40% nylon. A mid-range of medium permeabilitiesmay be obtained using from about 30-50% nylon and 70-50% EVOH. Thismultilayer film of the present invention surprisingly has a very thinnylon: EVOH core layer which is between 0.05 to 0.10 mils thick and lessthan 10% of the total thickness of the multilayer film, which core layeris connected to surface layers on opposing sides by intermediateadhesive layers each preferably having less than 10% of the total filmthickness, and this film having these characteristics may surprisinglybe made by using a biaxial stretching process such as that disclosed inU.S. Pat. No. 3,456,044 (Pahlke) with optional irradiative crosslinkingafter stretching.

[0096] This EVOH blend core layer will also control the oxygenpermeability of the film. For hard or semi-hard respiring cheesepackaging, the oxygen (O₂) permeability desirably should be minimized.Typical films will have an O₂ permeability of less than about 800 cm³/m²for a 24 hour period at 1 atmosphere, 0% relative humidity and 23° C.,and preferably less than 300 cm/m². For the blends of the presentinvention the O₂ transmission rate (O₂GTR) does increase as the CO₂ rateincreases although not to the same degree. For the desired CO₂permeabilities it has been found than an O₂ transmission rate(permeability) of at least about 40 cm³/m² at 24 hours, 1 atmosphere 0%relative humidity and at 23° C. is required, for medium high or higherCO₂ permeability the O₂GTR will preferably be greater than 75 cm³/m² for24 hours at 1 atmosphere, 0% relative humidity and 23° C., and for highCO₂ permeability films the O₂ permeability rate will preferably be atleast 150 cm³/m² or greater.

[0097] These former performance levels (<800 cm³/m² and <300 cm³/m²) aredesirable for shrink packaging foodstuffs such as cheeses which aresusceptible to contamination with undesirable molds which flourish inthe presence of oxygen.

[0098] The second and third adhesive layers of this film contain thenext most expensive components (relative to the EVOH:nylon blend corelayer). Advantageously, films according to the present invention,including heat shrinkable films having high shrinkage values may be inwhich each adhesive layer comprises only between about 2-10%, preferablyless than 5%, eg. about 2.5-3.0% of the multilayer film thickness. Useof a 3% adhesive layer directly adhered to either side of the core layerproduces a film which is extremely resistant to delamination and whichmay be oriented to produce film having high shrinkage of 30% or higherat 90° C. or less.

[0099] The following are examples and comparative examples given toillustrate the present invention.

[0100] Experimental results of the following examples are based on testssimilar to the following test methods unless noted otherwise.

[0101] Tensile Strength: ASTM D-882, Method A

[0102] % Elongation: ASTM D-882. Method A

[0103] Haze: ASTM D-1003-52

[0104] Gloss: ASTM D-2457, 450 angle

[0105] 1% Secant Modulus: ASTM D-882, Method A

[0106] Oxygen Gas Transmission Rate (O₂GTR): ASTM D-3985-81

[0107] Water Vapor Transmission Rate (WVTR): ASTM F 1249-90

[0108] Elmendorf Tear Strength: ASTM D-1992

[0109] Gauge: ASTM D-2103

[0110] Melt Index: ASTM D-1238, Condition E (1900)

[0111] Melting point: ASTM D-3418, DSC with 5° C./min heating rate

[0112] Carbon Dioxide Gas Transmission Rate (CO₂GTR): Carbon dioxide gaspermeability of film was measured by using an infrared sensor andrecorder which is available under the trademark Permatran C-IV by MoconTesting of Minneapolis, Minn., U.S.A. Each tubular film is cut open toform a flattened sheet. A single thickness of each film sheet is clampedbetween upper and lower halves of a diffusion cell having dimensionsdefining a 50 cm² test area. Carbon dioxide gas (100%) is placed intothe upper halve of the diffusion cell. A nitrogen carrier gas, which isfree of carbon dioxide, is flushed into the bottom halve of thediffusion cell. This cell is then connected to an infrared sensor andpump creating a closed loop for circulation of the trapped nitrogencarrier gas. The infrared sensor monitors increases in concentration ofCO₂ as carbon dioxide diffuses through the test film into the closedloop of nitrogen gas, and presents a voltage trace on a strip chartrecorder. This trace represents the amount of carbon dioxide diffusing.The carbon dioxide gas transmission rate is derived from the slope ofthe voltage trace; the instrument having been calibrated by recordingvoltage changes which correspond to measured amounts of CO₂ injectedinto the instrument.

[0113] Shrinkage Values: Shrinkage values are defined to be valuesobtained by measuring unrestrained shrink at 90° C. (or the indicatedtemperature if different) for five seconds. Four test specimens are cutfrom a given sample of the film to be tested. The specimens are cut intosquares of 10 cm length in the machine direction by 10 cm. length in thetransverse direction. Each specimen is completely immersed for 5 secondsin a 90° C. (or the indicated temperature if different) water bath (orsilicone oil if the test temperature is greater than 100° C.). Thespecimen is then removed from the bath and the distance between the endsof the shrunken specimen is measured for both the M.D. and T.D.directions. The difference in the measured distance for the shrunkenspecimen and the original 10 cm. side is multiplied by ten to obtain thepercent of shrinkage for the specimen in each direction. The shrinkagefor the four specimens is averaged for the M.D. shrinkage value of thegiven film sample, and the shrinkage for the four specimens is averagedfor the TD shrinkage value.

[0114] Shrink Force: The shrink force of a film is that force or stressrequired to prevent shrinkage of the film and was determined from filmsamples taken from each film. Four film samples were cut 1″ (2.54 cm)wide by 7″ (17.8 cm) long in the machine direction and 1″ (2.54 cm) wideby 7″ (17.8 cm) long in the traverse direction. The average thickness ofthe film samples was determined and recorded and a strip chart recorderwas calibrated at 0 gram and at 1,000 grams full scale load. Each filmsample was then secured between the two clamps spaced 10 cm apart. Oneclamp is in a fixed position and the other is connected to a straingauge transducer. The secured film sample and clamps were then immersedin a silicone oil bath maintained at a constant, elevated temperaturefor a period of five seconds. During this time, the force in grams atthe elevated temperature was read from the strip chart and this readingwas recorded. At the end of this time, the film sample was removed fromthe bath and allowed to cool to room temperature whereupon the force ingrams at room temperature was also read from the strip chart andrecorded. The shrink force for the film sample was then determined fromthe following equation wherein the results is obtained in grams per milof film thickness (g/mil):

Shrink Force (g/mil)=F/T

[0115] wherein F is the force in grams and T is the average thickness ofthe film samples in mils.

[0116] Impulse Seal Range:

[0117] The impulse sealing range test determines the acceptable voltageranges for impulse sealing plastic films. A Sentinel Model 12-12ASlaboratory sealer manufactured by Packaging Industries Group, Inc.,Hyannis Mass., U.S.A. was used. This impulse sealer is equipped with areplacement sealing ribbon for a Multivac AG100 brand packaging machine.The ribbon is available from Koch Supplies of Kansas City, Mo. In thistest, two four inch wide (T.D. direction) samples are cut from a tubularfilm. The impulse sealer is equipped with controls for coolant flow,impulse voltage and time, and seal bar pressure. These controls exceptfor impulse voltage are set at the following conditions: 0.5 secondsimpulse time (upper ribbon only) 2.2 seconds cooling time 50 psi (345kPa) jaw pressure 0.3 gallon per minute (1 liter per minute) of cooling(about 75° F. (22° C.)) water flow

[0118] One of the samples is folded in half for use in determining aminimum sealing voltage. This folding simulates folding which mayinadvertently occur during conventional bag sealing operations. Thefolded sample which now has four sheets or portions of film (hereinafterreferred to as “sheet portions”) is placed into the sealer and by trialand error the minimum voltage to seal the bottom two sheet portions toeach other was determined.

[0119] The maximum voltage is then determined for a sample having twosheet portions by placing it in the sealer and then activating the sealbar. The film sample is manually pulled with about 0.5 lbs. of force andthe voltage which does not cause burn through or significant distortionof the seal is determined.

[0120] Gassing Test: The Gassing Test is an evaluation of film adherenceto a vacuum packaged respiring natural cheese. In this test arectangular block of respiring natural cheese is vacuum packaged in afilm which is hermetically sealed. Due to microbiological activity manynatural cheeses such as emmental (swiss) respire or give off CO_(2.)Therefore, over time CO₂ gas will build up in a sealed film packageunless the film is permeable to CO_(2.) This build up of gas willinflate the sealed package if the rate of CO₂ generation is greater thanthe rate of permeability CO₂ through the film wall. The amount ofinflation will depend upon both the gas production rate and the filmpermeability or gas transmission rate. Film adherence to the surface ofthe packaged cheese is visually evaluated and given a numerical valuefrom 0 to 10, with greater value numbers indicating less adherence andmore ballooning. 0=complete film adherence to the cheese product. 5=filmballooned on flat sides, but product corners and edges in contact withfilm, 7=film ballooned away from all surfaces except corners,10=complete film ballooning away from all product surfaces includingflat sides, edges and corners. The same person evaluates all packages ina test to ensure accuracy. Evaluations are made over time and the timeelapsed for each evaluation is reported, generally in days. The packagedcheeses are all held at about 35° F. (˜2° C.) over the evaluationperiod. Standard deviation for multiple examples may be reported as maydifferences (A) in values for particular packages from one testevaluation over time to the next evaluation.

[0121] Following are examples and comparative examples given toillustrate the invention.

[0122] In all the following examples, unless otherwise indicated, thefilm compositions were produced generally utilizing the apparatus andmethod described in U.S. Pat. No. 3,456,044 (Pahlke) which describes acoextrusion type of double bubble method and in further accordance withthe detailed description above. All percentages are by weight unlessindicated otherwise.

EXAMPLES 1-6

[0123] In Examples 1-3, three biaxially stretched, heat shrinkable,multilayer films of the present invention were made. The layers of eachmultilayer film were coextruded and biaxially stretched according to acoextrusion type of tubular orientation process.

[0124] Examples 1-3 are five layered films. However, films of six ormore layers are also contemplated by the present invention. Theinventive multilayer films may include additional layers or polymers toadd or modify various properties of the desired film such as heatsealability, interlayer adhesion, food surface adhesion, shrinkability,shrink force, wrinkle resistance, puncture resistance, printability,toughness, gas or water barrier properties, abrasion resistance andoptical properties such as gloss, haze, freedom from lines, streaks orgels. These layers may be formed by any suitable method includingcoextrusion, extrusion coating and lamination.

[0125] For Examples 1-3, one extruder was used for each layer and theheat plastified resins from each extruder were introduced to a 5 layerspiral plate coextrusion die from which the resins were coextruded at aninner/first adhesive/core/second adhesive/outer layer thickness ratio ofabout 63:3:3:3:28 for Examples 1-3.

[0126] In Examples 1-3, for each layer, the resin or resin mixture wasfed from a hopper into an attached standard single screw extruder wherethe resin and/or mixture was heat plastified and extruded through a fivelayer coextrusion spiral plate die into a primary tube. The extruderbarrel temperatures for the core layer was about 400° F. (204° C.) andfor the first and second adhesive layers were about 370° F. (188° C.)and for the inner and outer layers were about 300° F. (149° C.). Theextrusion die had an annular exit opening of 3 inch diameter with a0.060 inch gap (7.62 cm×0.152 cm). The coextrusion die temperatureprofile was set from about 400° F. to 420° F. (204° C.-216° C.). Theextruded multilayer primary tube was cooled by spraying with unheatedtap water (about 12-24° C.).

[0127] The cooled primary tube was flattened by passage through a pairof nip rollers whose speed was controlled to neck down the primary tubeto adjust the tube circumference or flat width. In Examples 1-3, aflattened tube of about 3 inches (7.62 cm) flat width and about 21 mil(0.0533 cm) thickness was produced. The cooled flattened primary tubewas reheated, biaxially stretched, and cooled.

[0128] The cooled film was flattened and the biaxially stretched andbiaxially oriented film was wound on a reel. The machine direction(M.D.) draw or orientation ratio was about 3.75 and the transversedirection (T.D.) bubble or orientation ratio was about 3.0 for all thefilms. The draw point or orientation temperature was below thepredominant melting point for each layer oriented and above that layer'sglass transition point. Draw point temperature, bubble heating andcooling rates and orientation ratios are generally adjusted to maximizebubble stability and throughput for the desired amount of stretching ororientation. The resultant films of Examples 1-3 were biaxially orientedand had an excellent appearance. These films were all irradiated at alevel of 3.3 Mrad by electron beam after orientation and according tomethods well known in the art to cause crosslinking, especially of theinner and outer polymeric layers.

[0129] For all of the Examples 1-3, the inner layer (which was theinterior surface of the tubular film) comprised 100% by weight of anethylene vinyl acetate copolymer having a vinyl acetate content of10.5%, a density of 0.934 g/cm², a melt index of 0.3 g/10 min., andwhich is commercially available under the trademark LD701 from ExxonChemical Company of Houston, Tex., U.S.A.

[0130] The outer layer of Examples 1-3 (which was the exterior surfaceof the tube) also contained the same EVA as the inner layer but as acomponent of a blend. In Examples 1 and 2, 76% of the EVA copolymer wasblended with 20% of a very low density polyethylene sold by Dow ChemicalCompany of Midland, Mich., U.S.A. under the trademark Attane XU 61520.01which is a copolymer of ethylene and octene-1 having a melt index ofabout 0.5 dg/min and a density of about 0.912 g/cm³, with a Vicatsoftening point of 95° C. and a melting point of about 123° C. Also inthe outer layer blend of EVA and VLDPE is 4% by weight of afluoroelastomer processing aid sold under the trademark Ampacet 100031by Ampacet Corp. of Tarrytown, N.Y., U.S.A. The outer layer for Example3 was similar to that of Examples 1 and 2, but contained 44.3% of theabove noted VLDPE; 36.3% of the EVA copolymer, 4.4% of the processingaid and as an added constituent contained 15% of an ethylenealpha-olefin plastomer-type copolymer believed to be an ethylenebutene-1 copolymer having a reported melting point of 71° C. and soldunder the trademark Tafiner A-1085 by Mitsui Petrochemical Industries,Ltd. of Tokyo, Japan.

[0131] For Examples 1 and 2, the first adhesive layers were identicalblends of 30% of the same EVA copolymer used in the inner layer with 40%of a very low density polyethylene which is a copolymer of ethylene andoctene-1 copolymer having a density of about 0.912 g/cm3, a melt indexof about 0.5 dg/min., and which is sold under the trademark AttaneXU61509.32 by Dow Chemical Company of Midland, Mich., U.S.A. The firstadhesive layer, in addition to the above 30% EVA and 40% VLDPE,contained 30% of an extrudable anhydride modified linear low densitypolyethylene based tie layer resin having the following reportedproperties: density of 0.925 g/cm³, melt index of 2.0 dg/min., a meltingpoint of about 125° C., a vicat softening point of about 102° C., and isavailable under the trademark Plexar® PX360 from Quantum ChemicalCorporation, Cincinnati, Ohio, U.S.A. The second adhesive layer of eachof Examples 1 and 2 was identical to the corresponding first adhesivelayer. For Example 3, the first and second adhesive layers were also ablend of the same three components used in Examples 1 and 2, but indifferent amounts, For Example 3, the first and second adhesive layerscontained identical blends of 52.5% VLDPE, 17.5% EVA and 30% of theanhydride modified LLDPE resins.

[0132] For Example 1, the core layer comprised a 80:20 percent by weightblend of a saponified ethylene-vinyl acetate copolymer (EVOH) with anylon. A premix was formed by blending 80% EVOH with 20% nylon. Thispremixed blend was then added to an extruder hopper for extrusion as thecore layer. The EVOH was a commercially available copolymer sold by EvalCompany of America of Lisle, Ill., U.S.A. under the trademark EVAL G110Aand had a reported ethylene content of 48 percent by weight, and a meltindex of 14 dg/min and a melting point of 158° C. The nylon was acommercially available nylon 6/66 copolymer sold by Allied ChemicalCompany under the trademark Capron Xtraform XPN1539 and had a reportednylon 6 content of 85 mole % and nylon 66 content of 15 mole % with aDSC melting point of about 195° C., and a density of 1.13 g/cm³.

[0133] For Examples 2 and 3, the core layer constituents were the sameas those used in Example 1, but the relative amounts were different. InExample 2, 60% EVOH was blended with 40% nylon 6/66 copolymer. InExample 3, 30% EVOH was blended with 70% nylon 6/66 copolymer.

[0134] Comparative Examples 3-6 are not of the invention, but are priorart examples of commercial films used for packaging cheese. Thecomparative film of Example 4 is believed to be a four layer film of thestructure EVA/EVA/PVDC/EVA, whereas comparative Examples 5 and 6 arebelieved to be three layer films with Example 5 having a structure ofEVA/nylon:EVOH blend/ionomer and Example 6 having a structure ofionomer/polyethylene/nylon. All of these comparative examples are heatshrinkable.

[0135] Layer formulations of Example 1-6 are reported in Table 1.Physical properties of the films of Examples 1-6 were measured and arereported in Tables 2 and 3. TABLE 1 1st Adhesive Core Layer 2nd AdhesiveEx. No. Inner Layer Layer Composition* Layer Outer Layer 1 100% EVA 40%VLDPE 80% EVOH Same as 1st Ad 20% VLDPE 30% EVA 20% Nylon Layer 76% EVA30% Anhydride (3%) 4% Processing Aid Modified (0.07 mil)† LLDPE 2 100%EVA 40% VLDPE 60% EVOH Same as 1st Ad 20% VLDPE 30% EVA 40% Nylon Layer76% EVA 30% Anhydride (3%) 4% Processing Aid Modified (0.08 mil)† LLDPE3 100% EVA 52.5% VLDPE 30% EVOH Same as 1st Ad 44.3% VLDPE 17.5% EVA 70%Nylon Layer 36.3% EVA 30% Anhydride (3%) 15% Plastomer Modified (0.07mil)† 4.4% Processing Aid LLDPE 4 EVA EVA PVDC — EVA (5%) (0.1 mil) 5EAA — Nylon:EVOH — Ionomer (21-24%) (0.6-0.7 mil) 6 Ionomer —Polyethylene — Nylon** (54-59%) (1.3-1.6 mil) # thickness for the layer.# O₂ permeabilities.

[0136] The results in Table 2 demonstrate that films according to thepresent invention have good physical properties. The tensile strengthproperties of Examples 1-3 of the invention are comparable to thecommercially available films for packaging cheese of comparative Example4. Although comparative Example 6 is stronger than the films of theExamples 1-3, all of the inventive films have adequate and excellentstrength for many utilities including packaging of foodstuffs includingcheeses. The elongation at break values of the Examples 1-3 are similarto those reported for a film similar to comparative Example 4, and arelower than the values reported for comparative Examples 5 and 6. Forpackaging articles such as cheeses, the reported elongation at breakvalues for the example films of the invention have very goodextensibility which is adequate to accommodate any stretchingencountered under typical packaging and process conditions.

[0137] The shrinkage values for Examples 1-3 are very good especiallyfor a film containing EVOH. The transverse direction values are all near50% at 90° C. and shrinkage at lower temperatures of 85° C. and 80° C.are all superior to the 90° C. shrinkage values for comparative Example5. Although shrinkage values for comparative Example 5 were not measuredat the lower temperature, it would be expected in the art that suchvalues would be less than the values obtained at a higher temperature.Therefore the inventive films may have desirably high shrinkage valueswhich may be greater than 20% in either or both directions at 90° C. andbeneficially may be greater than 30%. Examples 1-3 had values measuredin excess of 35% in the machine direction (MD) as well as the transversedirection. High shrinkage especially at 90° C. or lower is an advantagein packaging articles such as hard or semi-hard cheese to provide closecontact between the film and the enclosed article surface which preventsor lessens damage which may be caused by contact with oxygen or bymovement of the article within the package. A further advantage of theinvention relative to the prior art EVOH containing film of Example 5 isthat good shrinkage values may be obtained at a lower temperaturethereby using a shrinking process which has lower energy requirements.Perhaps more importantly where the packaged article is a foodstuff, lowtemperature shrinking reduces exposure of the foodstuff to highertemperatures which may produce sensory defects and/or promoteundesirable growth of pathogenic or spoilage microbes including bacteriaor molds.

[0138] Unrestrained shrinkage values were also obtained at a very hightemperature of 220° F. (104° C.) for the examples of the invention.Example 1 has a shrinkage value at 220° F. (104° C.) of 54% in themachine direction (MD) and 53% in the transverse direction (TD). ForExample 2 these respective values at 104° C. were 57% MD/52% TD and forExample 3 shrinkage values were 53% MD/53% TD at 104° C. These valueswere obtained for comparison to those values obtained and reported inExamples 5-8 of European Patent Application 457,598 where the filmshaving EVOH:nylon blend core layers all had reported shrinkage values at104° C. which were substantially less than those values obtained withthe present invention. The highest value was reported in Example 7 ofthe European Application and had reported MD/TD shrinkage values of24%/30%.

[0139] Also the shrink forces reported for Examples 1-3, especially theresidual shrink forces, are at levels desirable to hold the film inclose contact with the enclosed article not only during possibleprocessing subsequent to packaging e.g. pasteurization, but also at roomtemperature. The residual shrink force at room temperature is importante.g. when a package may be opened exposing one end to the deleteriouseffects of exposure to the environment. Films and bags having a highresidual shrink force such as those values reported for Example 1-3 ofthe invention have continued close contact between film and article evenafter opening. The measured values of Examples 1-3 indicate that thefilm would be kept in close contact with an enclosed article andcontinue to maintain its protective functions. For example, when theenclosed article is a cheese, close contact with film after loss of avacuum within the package will lessen moisture loss (and thereforeweight loss) and minimize growth of aerobic organisms including molds.Growth of undesirable molds leads to waste because these moldy portionsare often cut away and discarded, while moisture loss leads to dried outportions which have an undesirable texture which may become so hard thatagain portions of the cheese are cut away and discarded. Of courseexposure of the surface of a cheese to the atmosphere (as often happenswhen a nonshrink film or a film having no or low residual shrink isemployed) may facilitate the cheese acquiring an off taste or odor whichis disagreeable. TABLE 2 TENSILE ELONGATION STRENGTH × SHRINK FORCE AvgAT BREAK 10³ psi SHRINK SHRINK SHRINK at 90° C. at RT GAUGE FLAT % at RTat 90° C. at 85° C. at 80° C. gm/mil gm/mil Ex. mil WIDTH at RT (mPa) %% % (Kg/cm) (Kg/cm) No. (micron) (mm) MD/TD MD/TD MD/TD MD/TD MD/TDMD/TD MD/TD 1 2.27 260 168/129 9.1/6.7 38/49 27/41 22/33 163/147 78/85(57.7) (63/46) (64/58) (31/33) 2 2.53 337 137/166 9.3/6.7 37/48 26/4119/33 148/122 61/92 (64.3) (64/46) (58/48) (24/36) 3 2.28 267 157/1258.3/7.7 36/48 28/40 21/32 128/157 59/88 (57.9) (58/53) (50/62) (23/35) 42.15 270  206/108†  8.7/7.1† 51/56 ND ND ** ** (54.6) 5 2.90 219 398/5806.0/6.4 16/12 ND ND ND ND (73.7) 6 2.41 92 607/804 10.7/9.9  33/17 ND ND*** *** (61.2)

[0140] TABLE 3 CO₂GTR† CO₂GTR† O₂GTR† GLOSS IMPULSE EX. at 5° C. at 20°C. at RT HAZE AT 45° SEAL RANGE No. 0% RH 0% RH 0% RH WVTR†† % ANGLE(VOLTS) 1 106-119* 268-288*  54 25 6.7 76 29-49 (61)** (53) 2 194-322*462-752*  81 22 6.7 75 28-48 (61)** (58) 3 481-564* 1110- 167 22 5.1 7929-46 1260* (56)** (53) 4 ND ND 357 25*** 7.4 74  32-50+ (48) (53) 5 NDND 147 9 ND 24 29-36 (69) (69) 6 ND ND 310 26 26.8 43 26-29 (52) (56)

[0141] Referring now to the film formulations listed in Table 1 and theproperties and test results reported in Table 3, it is seen thatdecreasing the amount of EVOH and increasing the amount of nylon in thecore layer blend produces films have a greater permeability to gasessuch as carbon dioxide and oxygen. The permeability of CO₂ was measuredat both 5° C. and 20° C. with the lower temperature representing atypical refrigeration temperature for foodstuffs such as cheese.Advantageously, the oxygen permeabilities for the inventive films ofExamples 1-3 are much lower than the O₂GTR for the comparative film ofExample 4 which has a chlorine containing polyvinylidene chloridebarrier layer and also much lower than the O₂GTR for the comparativefilm of Example 6 which is believed to rely upon an outer nylon layerfor its barrier properties. EVA, polyethylene and ionomer resins aregenerally not classed as gas barrier polymers and are known to be verypermeable to both oxygen and carbon dioxide. In all of the examples thelayers containing PVDC, EVOH and/or nylon are believed to be the gaspermeability rate controlling layer. Interestingly, comparative Example5 has an oxygen permeability (O₂GTR) similar to that measured for theinventive film of Example 3.

[0142] The films of the invention in Examples 1-3 all had a carbondioxide transmission rate (CO₂GTR) at 1 atmosphere at 24 hours, and 0%relative humidity which was at least 100 cm³/m² at 5° C. and at 20° C.the CO₂GTR was at least 250 cm³/m². In Examples 1-3 the CO₂GTR for thehighest CO₂ permeability film of the invention (Example 3) was at least400 cm³/m² at 5° C. and at least 900 cm³/m² at 20° C. (both at 24 hours,1 atmosphere and 0% relative humidity). The CO₂ permeability film ofExample 2 had a CO₂GTR of at least about 200 cm³/m² at 5° C. and atleast 450 cm³/m² at 20° C. (both at 24 hours, 1 atmosphere and 0%relative humidity). The room temperature (about 20-23° C.) O₂GTR of theinventive Examples 1-3 were above 50 cm³/m² for all the Examples (1-3)with Example 2 being above 75 cm³/m² and the high CO₂ permeability filmof Example 3 having a value above 100 cm³/m² (all at 1 atmosphere, 0%relative humidity for 24 hours). Also, the O₂GTR values for these threeexamples of the invention (1-3) were all less than 200 cm³/m² at roomtemperature (about 20-23° C.), 1 atmosphere, 0% relative humidity and at24 hours.

[0143] The nylon:EVOH blend core layer of the film of comparativeExample 5 was determined to be about 0.6-0.7 mil (15-18 microns) thickcompared to about 0.07 mil±0.01 (1.8 microns±0.2) for Examples 1-3.Therefore the invention obtains an equivalent oxygen barrier with abarrier layer which is {fraction (1/10)} as thick as that found incomparative Example 5. The nylon component of the Example 5 film had amelting point of (˜193° C.) and the EVOH component had a melting point(˜172° C.). Spectrographic analysis indicated that nylon was a majorcomponent of the blend while EVOH was indicated to be a minor component.

[0144] Furthermore, all of the Examples 1-3 of the invention exhibitedmuch higher shrinkage values than those of Example 5. The film ofExample 5 contained a relatively thick core layer of nylon and EVOHwhich constituted about 21-24% of the thickness of the multilayer film.Advantageously the present invention as embodied in Example 3 utilizedan economically thin core layer which provided a similar oxygenpermeability to comparative Example 5, but much superior shrinkagevalues at 90° C., superior optics and a broader sealing range. Theinventive films of Examples 1 and 2 also provide gloss values which aresignificantly better and sealing ranges which are significantly widerthan corresponding properties of the comparative film of Example 5. Thewide sealing range permits the inventive film to be heat sealed athigher temperatures without burn through than the prior art film. Theexamples of the invention also have better optical properties which givea better appearance as indicated by the gloss values. The inventivefilms have a better appearance including high gloss, and low haze withvery good clarity for an EVOH containing film. The haze of comparativeExample 5 was not determined because the sample contained a colorantwhich would have produced a high haze value regardless of the inherenthaziness of the film relative to the clear film samples of the inventionwhich did not contain any added colorants. The water vapor transmissionrates of Examples 1-3 had similar values to the comparative Examples 4and 6, but were higher than the measured value for comparative 5. All ofthe water vapor transmission rates were acceptable for packaging cheeseand no noticeable weight loss differences between the examples were seenin tests 7-18 as discussed below.

[0145] The ionomer/polyethylene/nylon film of comparative Example 6 hada higher oxygen permeability than the films of Examples 1-3, a poorerappearance as demonstrated by the high haze and low gloss values and anundesirably narrow heat sealing range. Example 6 also used the relativeexpensive ionomer resin as a main component of its inner sealing layer.

[0146] Comparative Example 4, which is a commercially available andacceptable film used for packaging cheeses also had a higher oxygenpermeability than the films of the invention. This comparative film hadan EVA/EVA/PVDC/EVA structure which had a chlorine-containing polymer.The inventive films are free from chlorine-containing polymers andtherefore are more readily incinerated or recycled.

EXAMPLES 7-12

[0147] In these examples weight loss, mold growth and gassing ofemmental type (swiss) cheese sealed in bags made from the films ofExamples 1-3 of the invention were tested along with a control barrierfilm and two commercially available cheese packaging films. Swiss cheesewas chosen for this test because this type of cheese is known to producelarge quantities of carbon dioxide gas both during aging at the cheesefactory and after packaging for shipment and sale. The lower grade ofswiss cheese is generally believed to give off more gas than highergrades of swiss cheese, however, both (respire) great amounts of carbondioxide in the post-aging stage where the cheese has been packaged fordelivery to customers of the cheese manufacturer e.g. groceries,restaurants and institutions such as hospitals and schools.

[0148] In view of this high CO₂ respiration rate, packaging of swisscheese represents a difficult test for CO₂ permeable packaging. If apackaging film has a suitably sufficient CO₂ permeability to minimize oreliminate package pillowing or ballooning for swiss cheese, then it isbelieved that most other types of respiring cheeses could be packaged inthe same film without ballooning. Ballooning is considered a packagingdefect in that consumers perceive respiring products in balloonedpackages such as ballooned packages of cheese to be inferior anddefective. Therefore consumers are believed to be less likely topurchase such products notwithstanding the wholesomeness of the packagedproduct. Since ballooning is recognized to be a result of biologicalactivity it is often adversely viewed by the consumer even where suchbiological activity, is a normal characteristic of the product. Also,where ballooning is severe there is concern that the integrity ofpackage seals or clips could become impaired. Furthermore, ballooningseparates the film from the surfaces of the packaged foodstuff whichfacilitates mold growth in the presence of oxygen. Swiss cheese may bemade by variations of cheese making processes and the method employed tomake swiss or any particular cheese should not be considered as limitingthe present invention which provides an inventive film and use as acheese package. Common starter cultures may include Lactobacillusbulgaricus, Streptococcus thermophilous and Propionibacter shermanii. Asuitable method for making a swiss-type cheese is that disclosed in U.S.Pat. No. 2,494,636 which patent is hereby incorporated by reference inits entirety. Example 7 was a control film (not of the invention) whichwas an oxygen barrier, heat shrinkable, heat sealable, multilayer filmhaving an EVA inner layer, a plasticized vinylidene chloride copolymercore layer and an outer layer of a blend of about 20% VLDPE, 76% EVA and4% processing aid. Example 8 was a comparative example (not of theinvention) of a commercially available cheese packaging film having anEVA inner layer, an outer layer similar to that above in Example 7, anda vinylidene chloride copolymer core layer as in Example 7, but havingabout double the amount of plasticizer to increase gas permeability.

[0149] Example 9 was a comparative example (not of the invention) of acommercially available cheese packaging film known to be in commercialuse to package swiss cheese for retail sale. Example 9 is believed to besimilar in layer composition and construction to Example 4 of Table 3and also is believed to have similar properties to those disclosed abovefor Example 4. Examples 10-12 were examples of the invention and arebags made from films corresponding to those described above in Examples1-3 respectively. The bags of Examples 7-12 were divided into twoidentical sets for packaging two different grades of cheese. The secondset is renumbered 13-18 with the film used for Example 13 correspondingto that film used for 7, and the film 14 corresponding to film 8 and soon ending with film 18 being the same as film 12.

[0150] For Examples 7-18, various films were packaged with aged hardcheese (Swiss) made and packaged generally according to the followingdescription.

[0151] Cheese curd suitable for making swiss-type cheese was made usinga Lactobacillus bulgaricus starter culture in milk and was formed into100 lb. blocks and held for 24 hours in vats. Then to reduce the pH ofthe cheese a brine solution was added and maintained at about 45° F. (7°C.) for another 24 hours (an antimycotic agent was also added in thebrine). The pH adjusted blocks of cheese were then placed in barrierbags, evacuated and heat sealed. These barrier bags are believed to havebeen nonshrinkable bags having a vinylidene chloride copolymer oxygenbarrier layer with low gas permeabilities eg. having a very low oxygenpermeability (less than 15 cm³ per m²). The packaged blocks were held atabout 41° F. (5° C.) for 12 days and then further aged for 20-24 days atabout 72-74° F. (22-23° C.). The cheeses were then graded according tothe Wisconsin grading system and further aged between 12-28 days atabout 34-36° F. (1-2° C.)

[0152] After the above low temperature aging, the 100 lb. blocks wererecut into blocks weighing between 2-18 lb., graded again and packagedin the test bags of Examples 7-18. Examples 7-12 were all packages ofGrade A Swiss cheese, in which the cheese was graded according tostandards set by the State of Wisconsin, U.S.A. Examples 13-18 were anidentical set of bags corresponding to those used in Examples 7-12 andthese bags were used to package Grade C Swiss cheese.

[0153] Typically, seven or ten lb. blocks are cut from each 100 lb blockfor retail packaging, however for the present examples the cheese wascut to fit the various sized test bags of Examples 7-18. Cheeses werepackaged by placing each cheese (which had been held at a temperature ofabout 36° F. (2° C.) prior to packaging) into a test bag which was thenevacuated, clipped closed and briefly passed through a shrink tunnel setat a temperature of 202° F. (94° C.) for a few seconds to shrink thefilm around the enclosed cheese. The packaged cheeses were weighed andthen held at a temperature of about 36° F. (2° C.). Then the packagedcheeses were transported from the cheese plant to a test facility wherethey were evaluated one day after packaging for gassing and microbialgrowth. After this initial evaluation the packaged cheeses were storedat about 34° F. (1° C.) and reevaluated 27 days later and 63 days later.The results of these evaluations are listed in Tables 4 and 5. TABLE 4GRADE A CHEESE AVG. AVG. WEIGHT WEIGHT LOSS LOSS GASSING TEST* EX. FW(%) at (%) at # 1 # 2 NO. (mm) DAY 27 DAY 63 1 DAY 27 DAY Δ 63 DAY Δ 1DAY 27 DAY Δ 63 DAY Δ 7 238 <0.1 <0.1 3.0 6 3 6 0 3.0 5 2 6 1 8 248 <0.1<0.1 3.0 6 3 7 1 3.0 7 4 8 1 9 249 0.1 0.1 3.5 7 3.5 5 −2 3.5 7 3.5 5 −210 264 0.1 0.1 3.0 5 2 5 0 3.0 6 3 4 −2 11 335 0.1 0.1 3.0 5 2 4 −1 3.06 3 6 0 12 267 0.2 0.2 2.0 3 1 3 0 2.0 2 0 3 0

[0154] TABLE 5 GRADE C* AVG. AVG. WEIGHT WEIGHT LOSS LOSS GASSING TESTCO₂ GTR O₂ GTR EX. FW (%) AT (%) AT 1 DAY 27 DAY 63 DAY (5° C.) at RTWVTR† NO. (mm) DAY 27 DAY 63 AVG σ AVG σ AVG cm³/m²** cm³/m²** (g/m²) 13238 0.1 0.1 2.9 0.8 5.8 1.0 6.0  4  17  8 14 247 <0.1 0.3 3.3 1.3 5.82.1 6.4 109 116 19 15 249 0.1 0.1 3.5 0.8 6.0 0.8 7.4 90-93 217 20 16264 0.1 0.1 3.4 1.2 5.3 2.5 6.1 106-119  54 25 (61) 17 335 0.1 0.1 4.40.8 6.5 1.6 6.6 194-322  81 22 (61) 18 267 0.1 0.1†† 3.0 0.3 2.8 1.12.0*** 481-564 167 22 (56)

[0155] Referring now to Tables 4 and 5, the Gassing Test resultsdemonstrate that all of the cheese packages according to the presentinvention show excellent CO₂ permeability relative to the controlbarrier film of Examples 7 and 13, as well as the comparative commercialcheese films of Examples 8, 9, 14 and 15 which utilized a plasticizedPVDC core layer. The most permeable film was that of Examples 12 and 18whose average rating remained at 3 or below over the 63 day evaluationdemonstrating that the films was very permeable CO₂ by remaining welladhered to corners, edges and large portions of the flat surfaces. Thesehigh gas permeabilities, which are shown with regard to Grade A andGrace C swiss cheese, indicate the suitability and superior performanceof the inventive film of Examples 12 and 18 for packaging cheeses havinga high gassing rate including respiring hard cheeses and cheeses such asthose listed in Table A under the High CO₂ Permeability heading. Thecheese packages according to the invention of Examples 10, 11, 16 and 17indicate permeabilities as good as those found in presentlycommercialized films using PVDC gas permeability controlling layers andthese inventive films are well suited for packaging semi-hard respiringcheeses and cheeses of low to medium CO₂ permeability such as thoselisted under those headings in Table A.

[0156] For all of the Examples 7-18 there was no commerciallysignificant weight loss at either 27 days following packaging or at theevaluation made 63 days after packaging. The cheeses were also examinedby eye for mold growth and none was seen on any of the samples of theexamples 7-18 at either the 27 day evaluation or the 63 day evaluation.This demonstrates that the inventive films perform as well ascommercially used films containing PVDC with respect to weight loss andmold growth over the test period.

[0157] It is believed that the inventive film may be advantageouslyemployed to package other gas releasing foodstuffs besides cheeses, forexample, fruits or vegetables. In this regard the combination of highmoisture barrier properties with gas permeability would appear to bedesirable attributes for packaging of fruits and vegetables. Anotherutility is the packaging of fresh cut flowers or as a horticulturalfilm. Also, there may be industrial applications as an environmentallycompatible film.

EXAMPLES 19-21

[0158] Five layer tubular films designated here as Examples 19-21 weremade by a biaxial stretching orientation process. This process wassimilar to that disclosed above for making the films of Examples 1-3,but these films were not irradiated.

[0159] These examples demonstrate the effect of changing the molepercent ethylene content of the EVOH component of the core layer blend.In all of the examples below, a core layer blend of 80 wt. % EVOH and 20wt. % nylon 6/66 copolymer was used. In Example 19 of the invention anEVOH having an ethylene content of 48 mole % was used whereas inExamples 20 and 21 EVOH copolymers having ethylene contents of 44 and 38mole %, respectively, were employed.

[0160] The film of Example 19 had an inner heat sealable layer whichcomprised 100% by weight of an ethylene vinyl acetate copolymer whichwas sold by Union Carbide Corporation (UCC) of Danbury, Conn. U.S.A.under the trademark DQDA 6833. This EVA copolymer reportedly had a vinylacetate content of about 10% by weight, a melting point of about 98° C.(as measured by a differential scanning calorimetry (DSC), and areported melt index of 0.25 g/10 minutes. This same EVA resin was alsoemployed as 76.5% of a blend formulation which made up the outer layer.

[0161] In addition to EVA, the outer layer blend contained 19.1% of avery low density polyethylene (VLDPE) which is available from UCC underthe trademark DEFD 1192, and 4.4% of a processing aid. The VLDPE was anethylene-butene-1-hexene-1 terpolymer having a reported density of 0.912g/cm³, a melt index of 0.19 g/10 min., and a melting point (by DSC) ofabout 122° C.

[0162] The inner and outer layers are connected to opposing sides of acore layer (which comprises a blend of EVOH and nylon) by intermediateadhesive layers of identical composition. Both adhesive layers compriseda blend of 53% of the above noted VLDPE with 17% of the above noted EVAand 30% of an adhesive or tie layer resin which was commerciallyavailable from Quantum Chemical Corporation of Cincinnati, Ohio U.S.A.under the trademark Plexar 3741. This Plexar 3741 adhesive material isbelieved to be an anhydride modified ethylene copolymer adhesive havingan ethylene-butene-1 linear low density polyethylene base resin. Theadhesive resin has a reported melt index of 1.5 dg/min. at 190° C.according to ASTM D-1238 and a melting point of about 120° C.

[0163] The core layer controlled the permeability of the film withregard to gases such as oxygen and carbon dioxide. The core layercontained 80% by weight of an ethylene vinyl alcohol copolymer (EVOH)which was commercially available from EVAL Company of America (EVALCA)of Lisle, Ill., U.S.A. under the trademark EVAL G156. This EVAL G156EVOH resin reportedly has an ethylene content of 48 mole %, and a meltindex of 6.4 dg/min., and a melting point of about 158° C. Blended withthe EVOH of the core layer was 20% by weight of a nylon 6/66 copolymersold by Allied-Signal, Inc. of Morristown, N.J., U.S.A. under thetrademark Capron Xtraform 1539 (hereinafter “1539”). This 1539 nylon6/66 copolymer had a reported nylon 6 content of 85 mole %, a nylon 66content of 15 mole %, and a copolymer melting point by DSC of about 195°C. This inventive film of Example 19 has a five layer structure which,if one refers to the Plexar resin containing layers as Adhesive (Ad)layers, may generally be identified as 100% EVA/Ad/80% EVOH:20%nylon/Ad/76.5% EVA:19.1% VLDPE: 4.4% Proc. Aid. The 100% EVA layer isthe inner layer of the tubular film. This film has correspondingrelative layer thicknesses of 65%/3%/3%/3%/26% where the inner layer isthe thickest layer. The film of Example 19 was about 2.65 mils (67microns) thick and had a core layer thickness of about 0.08 mil (2microns).

[0164] For Examples 20 and 21 the inner and outer layers were identicalblends of: 70.6% VLDPE (DEFD 1192); 25% EVA (DQDA 6833); and 4.4% of aprocessing aid. These components were described more fully above withrespect to Example 19. The intermediate adhesive layers were identicalblends of: 52.5% VLDPE (XU61509.32); 30% adhesive (Plexar 3779); and17.5% EVA (DQDA 6833). This VLDPE (XU61509.32) was an ethylene-octene-1copolymer having a reported density of 0.912 g/cm³, a melt index of 0.5dg/min., and a melting point of about 123° C., which was available fromDow Chemical Company under the trademark ATTANE XU 61509.32. Theadhesive resin (Plexar 3779) is believed to be an anhydride modifiedethylene-hexene-1 linear low density polyethylene copolymer which wasavailable from Quantum Chemical Corporation under the trademark Plexar3779. The adhesive resin had a reported melting point of about 120° C.and melt index of 0.8 dg/min. The core layers of Examples 20 and 21 wereboth 80:20 weight percent blends of EVOH:nylon 6/66 copolymer. The nyloncopolymer was the same one used for Example 19. The EVOH copolymer usedin Example 20 had a reported ethylene content of about 44 mole percent,a melting point of about 165° C., and a melt index of 3.5 dg/min. at210° C. and was available from Nippon Synthetic Chemical Industry Co.(hereinafter “Nippon”) under the trademark Soarnol 4403. The EVOHcopolymer used in Example 21 had a reported ethylene content of 38 molepercent, a melting point of about 173° C., a melt index of 8 dg/min. at210° C., and was available from Nippon under the trademark Soarnol 3808.The films of the Examples 20 and 21 had similar layer thickness ratiosto that of Example 19. Various properties of the films of Examples 19-21were measured and are reported in Table 6 below. TABLE 6 TENSILE AVG.STRENGTH × SHRINK SHRINK EVOH GAUGE 10³ psi GLOSS at 90° at 80° C. EX.C₂ CONTENT mil at RT O₂GTR† HAZE at 45° % % NO. MOLE % (micron) (mPa) atRT % ANGLE MD/TD MD/TD 19 48 1.63  8.4/7.8 93 1.0 91 40/49  25/38*(41.4) (60) 20 44 2.57 10.7/8.7 28 6.3 71 20/37 11/26 (65.3) (69) 21 382.52 10.1/8.8  8 6.3 71 27/38 17/26 (64.0) (71)

[0165] Referring to Table 6, the oxygen permeability of each film ofExamples 19-21 was controlled by the core layer for each film. Each corelayer contained a blend of nylon and EVOH with the ethylene content ofthe EVOH varying from example to example. Example 19 of the invention(48 mole % Cs content) had a high gas permeability relative to Examples20 (44 mole % C₂ content) and 21 (38 mole % C₂ content) as shown by theroom-temperature oxygen permeabilities. The carbon dioxide permeabilityof Example 19 would be greater than the oxygen permeability followingthe relationship established above in Examples 1-3 which demonstratedthat CO₂ permeability of the inventive films are higher (generally about4-11 times higher) than oxygen gas transmission rates under the sametest conditions. Therefore, the higher oxygen permeability wouldindicate that the film of Example 19 may be suitably used to package arespiring foodstuff such as cheese. In contrast the films of Examples 20and 21 had much lower oxygen permeabilities (<40 cm³/m² at 24 hours, 1atmosphere, 0% relative humidity and at room temperature) with oxygenpermeability decreasing with a corresponding decrease in ethylenecontent. The film of Example 21 is a high barrier to oxygen whileExample 20 is an oxygen barrier layer. The inventive film of Example 19is permeable to oxygen at the stated conditions, but under refrigerationlow humidity conditions would have a lower oxygen permeability whilemaintaining a high CO₂ permeability making such film well suited forpackaging a respiring cheese as further shown in the following examples.

[0166] Disadvantageously, the barrier properties of films having a corelayer EVOH component with an ethylene content less than 48 mole percent(or a melting point higher than 158° C.) are too great to provide thedesired high CO₂ permeability for packaging respiring articles requiringa high CO₂ permeable film. However, EVOH resins having an ethylenecontent less than 48 mole % and as low as 38 mole % (or a melting pointhigher than 158° C. and as high as about 175° C.) may be blended withhigher amounts of nylon polymer up to about 70% by weight nylon toproduce films having sufficient permeability to package low and mediumpermeability CO₂ respiring articles such as gouda, edamer and butterkasecheeses. In addition, as shown in Table 6 the film of Example 19 hassuperior shrink values which are due in part to the high ethylenecontent EVOH which has a lower melting point relative to the EVOHcopolymer used in Examples 20 and 21. The EVOH melting point of 164° C.to 173-175° C. for Examples 20 and 21, respectively, are substantiallyabove that of PVDC which is commonly used with a plasticizer as thebarrier or gas permeability controlling layer of a heat shrinkablecheese film; the vinylidene chloride copolymers melt at about 148°-150°C. The higher melting EVOH polymers are relatively stiff and inflexibleat the substantially lower orientation suitable for stretch orienting ofthe generally lower melting components of the intermediate adhesivelayers and the inner and outer layer which frequently utilize suchresins as EVAs and various polyethylenes and ethylene-alpha-olefincopolymers. Therefore, the composition of the present invention mayadvantageously use a very thin but continuous core layer containing EVOHwhich is less than 10% of the total film thickness to facilitateorientation with the aforementioned polymers without requiring eitherexcessively thick adhesive layers (>10% of the multilayer filmthickness) or outer layer having a majority of their polymeric masscomprised of higher melting point polymers such as polypropylene,propylene-ethylene copolymers, and produce films having relatively highshrinkage values.

[0167] Also, Example 19 demonstrates that preferred embodiments of theinvention may advantageously use a lower melting point EVOH incombination with a nylon 6/66 copolymer to facilitate orientation of amultilayer film having polymers such as EVA which may have meltingpoints substantially lower than the melting point of the EVOH andproduce films having relatively higher shrinkage values and high shrinkvalues at lower temperatures compared to films made using EVOH polymershaving melting points higher than 158° C. The film of Example 19 hasexcellent low temperature shrinkage values of at least 25% in either orboth of the machine and transverse directions at not only 90° C., butalso at 80° C. The MD/TD values of 40/49 at 90° C. are more than 25%better than the best values measured for Examples 20 and 21 which alsoexhibit shrinkage values of 20-30% or more at 90° C.

[0168] The inventive film of Example 19 also exhibits good tensilestrength and has very good optical properties with desirably high glossand low haze values. The inventive film had a very low haze of about1.0% and a gloss of more than 90. Although not reported in Table 6, thepuncture resistance was also measured for these films and all films hadgood puncture resistance indicating that these films may also beusefully employed as an industrial shrink wrap having punctureresistance.

EXAMPLES 22-27

[0169] Example 22 is a comparative Example (not of the invention) of acommercially available heat shrinkable film having high CO₂ permeabilitywhich is used for packaging respiring cheeses. This film was in the formof a bag and was analyzed to be a three layer structure of EVA/PVDC/EVAhaving individual layer thicknesses of 1.3/0.1/0.6-0.7 with the thickerEVA layer being the inner surface layer of the bag. The PVDC layer wasthe gas transmission (permeability) controlling layer and wasplasticized to a sufficient extent that the film had a high CO₂ and O₂permeability. Physical properties of the film were measured and arereported below in Table 7. From the results presented in table 7 it isseen that the film of Example 22 has a very high CO₂ permeabilitysuitable for packaging articles requiring a high CO₂ permeability. Also,the shrinkage values at 90° C. and 80° C. are very good.Disadvantageously, the film optical properties are poor with a highlevel of haze and low gloss. A further disadvantage of this film is thatit employs a chlorine-containing polymer, PVDC, which is difficult torecycle and incinerate.

[0170] Examples 23-26 were all biaxially stretched tubular, heatshrinkable films made by process similar to that used for Examples 1-3above, however these films were not irradiated. The first outer layerwhich was the inner surface layer of the tube in each instance has apolymer composition which was essentially 100% EVA (DQDA 6833); thesecond outer layer (the outer protective surface layer of the tube) wasa blend of 66% of the same EVA with 30% of a VLDPE terpolymer (DEFD1192) and 4% of a processing aid (Ampacet 10003); the first and secondadhesive layers were identical in composition and comprised a blend of:40% EVA (6833), 30% VLDPE (1192) and 30% adhesive resin (Plexar PX169);the core layers all comprised an EVOH copolymer which was commerciallyavailable from EVALCA under the trademark G110A and had an ethylenecontent of 48 mole %. The core composition was varied from Example 23 to26 by blending in nylon 6/66 copolymer (1539) to form a core layercomposition having from 0 to 70 weight % nylon 6/66 copolymer. Example23 was a comparative example (not of the invention) which had 100% EVOH(G110A)in the core layer. The core layers for Example 24 of theinvention comprised 80% EVOH and 20% nylon; Example 25, 60% EVOH and 40%nylon; and Example 25, 30% EVOH and 70% nylon. All of the films wereprepared having a first outer layer/adhesive layer/core layer/adhesivelayer/second outer layer thickness ratio of 63/3/3/3/28. Physicalproperties of the unirradiated films were measured and are reported inTable 7. TABLE 7 SHRINK SHRINK CO₂GTR† O₂GTR† O₂GTR† at 90° C. at 80° C.GLOSS EX. CORE at 5° C. at 5° C. at RT % % HAZE AT 45° No. LAYER 0% RH0% RH 0% RH MD/TD MD/TD % ANGLE 22 PVDC 331-342 43 450  36/52 16/30 17.056 (58) (57) 23 EVOH 48-53  7 34 30/44 12/27 5.2 76 100% (58) (64) 24EVOH:NYLON 6/66 66-80 10 39 31/42 12/25 5.6 76 80:20% (58) (61) 25EVOH:NYLON 6/66 131-158 14 64 32/43 14/23 5.2 78 60:40% (64) (61) 26EVOH:NYLON 6/66 105-268 28 171  29/38 12/21 5.6 77 30:70% (58) (56) 27EVOH:NYLON 11 ND ND 64 44/53 ND 3.8 82 80:20% (53)

[0171] The multilayer films of Example 23-26 had typical thicknesseswhich were between about 2.2 and 2.5 mils thick. All had good lowtemperature shrinkage values which were suitable for heat shrinkpackaging of a variety of articles at 90° C. or lower temperatures. Thefilms also exhibited excellent optical properties with much lower hazeand higher gloss than was measured for the comparative commercialPVDC-containing film of Example 22. Advantageously, all of the films ofExamples 23-26 may be easily recycled, and may also be incineratedwithout producing chlorinated by-products. The oxygen-transmission ratefor Example 23 is low at both room temperature and 5° C. indicating agood gas barrier. The CO₂ gas transmission rate was undesirably low forpackaging CO₂ respiring articles. Example 24 had an oxygen permeabilityof about 40 cm³/m² at room temperature, but had a CO₂ permeability ratewhich was at least about 20% or more higher than for the gas barrierfilm of crosslinked Example 23. As previously shown in Examples 1-3(which were irradiated) as more nylon is blended into the EVOHcopolymer, the CO₂ and O₂ permeability may be adjusted providing greatergas permeation. Advantageously, addition of nylon greatly increases theCO₂ permeability relative to the increase in oxygen permeability. Thisis due in at least part to the permeability of EVOH to CO₂ being muchgreater than the permeability EVOH to oxygen. Therefore, permeabilitiesto CO₂ may be significantly increased while maintaining relatively lowlevels of ° 2 permeability. In other words if you multiply low and highnumbers by the same factor a greater numerical change is seen in thelarger number. Thus the difference in permeability rates is much largerfor blends of EVGH:nylon having large amounts of nylon than smalleramounts. Examples 24-26 of th invention all had O₂GTR values which wereat least 10 cm³/m² at SOC, Ok relative humidity, 1 atmosphere, at 24hours, and the corresponding O₂GTR values at room temperature (about20-23° C.) were 39 cm³/m² (about 40 cm³/m²) or higher.

[0172] Referring now to Example 27, a five layer multilayer, tubular,heat shrinkable, nonirradiated film was made as described above withrespect to Examples 23-26. The first outer layer (inner surface layer ofthe tube) was comprised of EVA (6833) while the second outer layercomprised about 74% of a first EVA having a vinyl acetate content ofabout 12 mole percent, a density of about 0.94 g/cm³, and melt index ofabout 0.35 dg/min. which was commercially available from DuPont underthe trademark Elvax 3135X blended with about 23.5% of a second EVAhaving a vinyl acetate content of about 4.5 mole percent, a density ofabout 0.93 g/cm³, a melt index of about 0.25 dg/min. which wascommercially available from Quantum under the trademark NA 3507 andfurther blended with about 2.5% of a processing aid (Ampacet 100031).The adhesive layers were identical and comprised a blend of 70% VLDPE(1192) with 30% by weight of an adhesive resin which is believed to bean anhydride modified butene-1 based LLDPE having a melt index of about1.5 dg/10 min. at 190° C., and a melting point of about 120° C. Thisadhesive resin was commercially available from Quantum Corp. under thetrademark Plexar 3741. The core layer comprised a blend of 80% by weightof an EVOH (EVALCA G115) having an ethylene content of about 48 molepercent, a melt index of 14.0 dg/min., and a melting point of 158° C.with 20% of a nylon 11 having a reported density of about 1.04 g/cm³which was commercially available under the trademark Besno from RilsanCorp. now believe to be Atochem North America, Inc. of Philadelphia,Pa., USA.

[0173] Physical properties of this film were measured and are reportedin Table 7 above. The film is seen to provide an oxygen permeability atroom temperature which indicates that the film should have good CO₂ gastransmission rates suitable for packaging high gassing respiringarticles. The measured optical property of haze was desirably low andthe film had good gloss. However, visual inspection of the filmindicated visible streaks and lines which detracted from the filmappearance. Such film of Example 27 is workable, but does not have thesame excellent appearance obtained with films of the invention whichutilize nylon 6/66 copolymer.

[0174] Films, bags and packages of the present invention may also employcombinations of characteristics as described in one or more of theclaims including dependent claims which follow this specification andwhere not mutually exclusive, the characteristics and limitations ofeach claim may be combined with characteristics or limitations of any ofthe other claims to further describe the invention.

[0175] The above examples serve only to illustrate the invention and itsadvantages, and they should not be interpreted as limiting since furthermodifications of the disclosed invention will be apparent to thoseskilled in the art in view of this teaching. All such modifications aredeemed to be within the scope of the invention as defined by thefollowing claims.

What is claimed is:
 1. A multilayer cheese packaging film having athickness of less than 10 mils and comprising a first outer layer; acore layer having a thickness between about 0.05 to about 0.10 milscomprising a blend of about 20-70 wt. % of nylon 6/66 copolymer andabout 30-80 wt. % of an EVOH copolymer having a melting point of about175° C. or lower; a protective second outer layer; and first and secondadhesive layers; wherein said barrier layer is between said first andsecond adhesive layers with (1) said first adhesive layer being adheredto a first surface of said core layer, said first adhesive layer beinglocated between said first outer layer and said core layer, and (2) saidsecond adhesive layer being adhered to an opposing second surface ofsaid core layer, said second adhesive layer being located between saidprotective second outer layer and said core layer; and wherein said filmis heat shrinkable at 90° C.
 2. A film, as defined in claim 1, whereinsaid film core layer comprises from 2 to 10 of the total film thickness.3. A film, as defined in claim 1, wherein said core layer thicknesscomprises less than 5% of said multilayer film thickness.
 4. A film, asdefined in claim 1, wherein said film adhesive layers each comprise athickness of 10% or less of said multilayer film thickness.
 5. A film,as defined in claim 1, wherein said film is a tube with said first outerlayer being an inner surface layer of said tube and said protectivesecond outer layer being an outer surface layer of said tube.
 6. A film,as defined in claim 1, wherein said film is formed as a bag with saidfirst outer layer being a heat sealable inner surface layer of said bagand said protective second outer layer being an outer surface layer ofsaid bag.
 7. A film, as defined in claim 1, wherein said EVOH copolymerhas a melting point of about 165° C. or less.
 8. A film, as defined inclaim 1, wherein said EVOH copolymer has a melting point of about 158°C. or less.
 9. A film, as defined in claim 1, wherein said EVOHcopolymer has a melting point of about 158° C.
 10. A film, as defined inclaim 1, wherein said film has a shrinkage value of at least 15% at 90°C. in at least one direction.
 11. A film, as defined in claim 1, whereinsaid film has a shrinkage value of at least 15% at 90° C. in bothmachine and transverse directions.
 12. A film, as defined in claim 1,wherein said film has a shrinkage value of at least 20% at 90° C. in atleast one direction.
 13. A film, as defined in claim 1, wherein saidfilm has a shrinkage value of at least 20% at 90° C. in both machine andtransverse directions.
 14. A film, as defined in claim 1, wherein saidfilm has a shrinkage value of at least 30% at 90° C. in at least onedirection.
 15. A film, as defined in claim 1, wherein said film has ashrinkage value of at least 30% at 90° C. in both machine and transversedirections.
 16. A film, as defined in claim 1, wherein said film has ashrinkage value of at least 35% at 90° C. in both machine and transversedirections.
 17. A film, as defined in claim 1, wherein said film has ashrinkage value of at least 20% at 80° C. in at least one direction. 18.A film, as defined in claim 1, wherein said film has a shrinkage valueof at least 20% at 80° C. in both machine and transverse directions. 19.A film, as defined in claim 1, wherein said film has a shrinkage valueof at least 30% at 80° C. in at least one direction.
 20. A film, asdefined in claim 1, wherein said film has a shrinkage value of at least25% at 85° C. in both machine and transverse directions.
 21. A film, asdefined in claim 1, wherein at least one of said outer layers comprisesEVA, VLDPE, EAA, or an ethylene-α-olefin copolymer having at least 80%of its polymeric units derived from ethylene, or blends thereof.
 22. Afilm, as defined in claim 1, wherein at least one said adhesive layerscomprises an anhydride modified polyolefin blended with EVA.
 23. A film,as defined in claim 1, wherein both of said adhesive layers comprises ananhydride modified polyolefin blended with EVA.
 24. A film, as definedin claim 1, wherein at least one of said adhesive layers comprises ananhydride modified polyolefin blended with a polyethylene.
 25. A film,as defined in claim 1, wherein both of said adhesive layers comprises ananhydride modified polyolefin blended with a polyethylene.
 26. A film,as defined in claim 1, wherein at least one of said outer layerscomprises polypropylene, a propylene ethylene copolymer, ionomer, nylon,polyethylene, an ethylene vinyl ester, a polyolefin, a LLDPE, an LMDPE,a LDPE, an HDPE, an elastomer, a plastomer, or blends of one or morethereof.
 27. A multilayer cheese packaging film comprising a heatsealing layer; a core layer having a thickness between about 0.05 toabout 0.10 mils comprising a blend of about 20-70 wt. % of nylon 6/66copolymer and about 30-80 wt. % of an EVOH copolymer having an ethylenecontent of about 38 mole percent or higher; an outer protective layer;and first and second adhesive layers; wherein said core layer is betweensaid first and second adhesive layers with (1) said first adhesive layerbeing adhered to a first surface of said core layer, said first adhesivelayer being located between said heat sealing layer and said core layer,and (2) said second adhesive layer being adhered to an opposing secondsurface of said core layer, said second adhesive layer being locatedbetween said protective layer and said core layer; and wherein said filmhas an oxygen transmission rate greater than 40 cm³/m² at 24 hours at 1atmosphere, 0% relative humidity and at about 73° F. (˜23° C.).
 28. Afilm, as defined in claim 27, wherein said film is irradiated.
 29. Afilm, as defined in claim 27, wherein said EVOH has an ethylene contentof at least 44 mole percent.
 30. A film, as defined in claim 27, whereinsaid EVOH has an ethylene content of at least 48 mole percent.
 31. Afilm, as defined in claim 27, wherein said EVOH has an ethylene contentof about 48 mole percent.
 32. A film, as defined in claim 27, whereinsaid film is a tube with said sealing layer being an inner layer andsaid protective layer being an outer layer of said tube.
 33. A film, asdefined in claim 27, wherein said film is heat shrinkable at 90° C. 34.A film, as defined in claim 27, wherein said film has a heatshrinkability of at least 30% at 90° C. in at least one direction.
 35. Afilm, as defined in claim 27 wherein said film has a CO₂GTR of at least250 cm³/m² at 1 atmosphere, at 20° C. and 0% relative humidity.
 36. Afilm, as defined in claim 35, wherein said film has a CO₂GTR of at least100 cm³/m² at 1 atmosphere, at 5° C. and 0% relative humidity.
 37. Afilm, as defined in claim 27, wherein said film has a CO₂GTR of at least400 cm³/m² at 1 atmosphere, at 24 hours, at 5° C. and 0% relativehumidity.
 38. A film, as defined in claim 27, wherein said film has ahaze value of less than 10%.
 39. A film, as defined in claim 27, whereinsaid film has a gloss at 45° C. which is greater than 65 H.U.
 40. Amultilayer cheese packaging film comprising a heat sealing layer; a corelayer having a thickness between about 0.05 to about 0.10 milscomprising a blend of about 20-70 wt. % of nylon 6/66 copolymer andabout 30-80 wt. % of an EVOH copolymer having an ethylene content of atleast about 48 mole percent; an outer protective layer; and first andsecond adhesive layers; wherein said core layer is between said firstand second adhesive layers with (1) said first adhesive layer beingadhered to a first surface of said core layer, said first adhesive layerbeing located between said heat sealing layer and said core layer, and(2) said second adhesive layer being adhered to an opposing secondsurface of said core layer, said second adhesive layer being locatedbetween said protective layer and said core layer; and wherein at leastone of said heat sealing layer and said protective layer is crosslinked.41. A film, as defined in claim 40, wherein said film is irradiated. 42.A film, as defined in claim 40, wherein said film is irradiated betweenabout 2.0 to 5 Mrad.
 43. A film, as defined in claim 40, wherein saidfilm outer layer is crosslinked.
 44. A film, as defined in claim 40,wherein said film is a tube with said sealing layer being an inner layerand said protective layer being an outer layer of said tube.
 45. A film,as defined in claim 40, wherein said film is formed as a bag with saidsealing layer being an inner surface layer of said bag and saidprotective layer being an outer surface layer of said bag.
 46. A film,as defined in claim 40, wherein said film is heat shrinkable at 90° C.47. A film, as defined in claim 40, wherein said film has a shrinkagevalue of at least 20% at 90° C. in at least one direction.
 48. A film,as defined in claim 40, wherein said film is biaxially stretched in twodirections and has a shrinkage value of at least 20% at 90° C. in bothdirections.
 49. A film, as defined in claim 40, wherein said nylon 6/66copolymer has a melting point of about 195° C.
 50. A film, as defined inclaim 40, wherein said core layer consists essentially of said blend ofEVOH and nylon.
 51. A film, as defined in claim 40, wherein said corelayer has a thickness of about 0.06 mils.
 52. A packaged cheesecomprising a cheese encased in a film, as defined in claim 40, whereinsaid film is formed into a bag.
 53. A film, as defined in claim 40,wherein said film is labelled to indicate that it is for use inpackaging cheese.
 54. A film, as defined in claim 40, wherein said filmhas a CO₂ gas transmission rate of between about 100 to 600 cm³/m² at 24hours at 1 atmosphere, 0% relative humidity and at 5° C.
 55. A film, asdefined in claim 40, wherein said film has a CO₂ gas transmission rateof at least 100 cm³/m² at 24 hours at 1 atmosphere, 0% relative humidityand at 5° C.
 56. A film, as defined in claim 55, wherein said film hasan O₂ gas transmission rate of 10 cm³/m² or higher at 24 hours, 1atmosphere, 0% relative humidity and 5° C.
 57. A packaged cheesecomprising a cheese encased in a multilayer film having in contact withsaid cheese an inner food contact layer, said multilayer film furthercomprising: an outer protective layer; first and second adhesive layers;and a core layer having a thickness between about 0.05 to about 0.10mils (1.27-2.54 microns); said core layer comprising a blend of about20-70 weight percent nylon and about 30-80% of an ethylene vinyl alcoholcopolymer having an ethylene content of about 48 mole percent, whereinsaid core layer is connected to said inner layer and said outer layer bysaid first and second adhesive layers, respectively.
 58. A packagedcheese, as defined in claim 57, wherein at least one of said inner andouter layers is crosslinked.
 59. A packaged cheese, as defined in claim57, wherein at least one layer of said film is irradiated.
 60. Apackaged cheese, as defined in claim 57, wherein said entire film is abiaxially stretched film, said entire film being irradiated afterbiaxial stretching.
 61. A packaged cheese, as defined in claim 57,whereas said cheese is emmental cheese.
 62. A packaged cheese, asdefined in claim 57, wherein said cheese is a natural cheese containinga starter culture of a CO₂ producing bacteria.
 63. A packaged cheese, asdefined in claim 57, wherein said cheese is gouda.
 64. A packagedcheese, as defined in claim 57, wherein said cheese is edam.
 65. Aprocess for making a biaxially stretched, heat shrinkable multilayerfilm having a thin core layer which controls oxygen and carbon dioxidepermeability of said film comprising: coextruding in a tubular form,around a volume of air, melt plastified polymeric resins having a firstouter layer, a core layer comprising a blend of EVOH and nylon, a secondouter layer, first and second adhesive layers wherein said core layer isbetween said first and second adhesive layers with (1) said firstadhesive layer being directly adhered to a first surface of said corelayer, said first adhesive layer being located between said first outerlayer and said core layer, and (2) said second adhesive layer beingdirectly adhered to an opposing second surface of said core layer, saidsecond adhesive layer being located between said second outer layer andsaid core layer to form a primary tube wherein said core layer and saidfirst and said second adhesive layers each comprise less than 10% of thetotal thickness of the primary tube; cooling and collapsing said primarytube; reheating said primary tube to an orientation (draw) temperature,simultaneously biaxially stretching said primary tube to form anexpanded, biaxially stretched, secondary tube having a continuous corelayer less than 0.10 mil in thickness; and rapidly cooling saidstretched film to form a heat shrinkable film.
 66. A process, as definedin claim 65, wherein said heat shrinkable film is irradiated after saidsending tube cooling step.
 67. A process, as defined in claim 65 whereinsaid core layer comprises less than 5% of said primary tube thickness.68. A process, as defined in claim 65 wherein said first and secondadhesive layers comprise less than 5% of said tube thickness and aredirectly adhered to said first and second outer layers, respectively.69. A multilayer cheese packaging film comprising a first outer layer; acore layer having a thickness between about 0.05 to about 0.10 milscomprising a blend of about 20-70 wt. % of nylon 11 and about 30-80 wt.% of an EVOH copolymer having an ethylene content of at least about 38mole percent; a second outer protective layer; and first and secondadhesive layers; wherein said core layer is between said first andsecond adhesive layers with (1) said first adhesive layer being adheredto a first surface of said core layer, said first adhesive layer beinglocated between said heat sealing layer and said core layer, and (2)said second adhesive layer being adhered to an opposing second surfaceof said core layer, said second adhesive layer being located betweensaid protective layer and said core layer.
 70. A film, as defined inclaim 69, wherein said film is irradiated.
 71. A film, as defined inclaim 69, wherein said film is heat sealable.
 72. A film, as defined inclaim 69, wherein said film has a core layer comprising a thickness lessthan 10% of the thickness of the entire film.
 73. A film, as defined inclaim 69, wherein said film is heat shrinkable at 90° C.